Some people don't believe that driving more slowly can save lives．But the truth is that driving more slowly can help a person to avoid serious accidents． The following chart shows the distance that 题目和参考答案——青夏教育精英家教网—

题目内容

Some people don't believe that driving more slowly can save lives．But the truth is that driving more slowly can help a person to avoid serious accidents．

The following chart shows the distance that it takes to stop a car at a given speed．The distance is measured in feet．The shaded area shows the driver's thinking distance．That's the distance it takes for the driver to react to a danger that he sees．The white area shows the car's braking distance．That's the distance it takes for the car to stop once the brakes（闸、刹车） are used．The number at the top of each bar shows the total number of feet that it takes to stop the car

1．According to the chart, what is the total number of feet needed to stop a car that is traveling at 50 miles per hour?

A．55． B．73． C．128． D．183．

2．What is the braking distance for a car that is traveling at 60 miles per hour?

A．66 feet． B．119 feet． C．185 feet． D．251 feet．

3．Which of the following statements about braking and speed is true?

A．The braking distance is what it takes for the driver to react to a danger that he sees．

B．The speed of a car has a direct effect on the distance needed to stop the car．

C．The braking distance increases only when a driver drives faster than 50 miles per hour

D．Driving slowly can help a person to avoid all accidents

1.D 2.C 3.B

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Can people change their skin colour without suffering like pop king Michael Jackson? Perhaps yes. Scientists have found the gene that determines skin colour.

The gene comes in two versions, one of which is found in 99 per cent of Europeans. The other is found in 93 to 100 per cent of Africans, researchers at Pennsylvania State University report in the latest issue of Science.

Scientists have changed the colour of a dark-striped zebrafish to uniform gold by inserting a version of the pigment(色素) gene into a young fish. As with humans, zebrafish skin colour is determined by pigment cells, which contain melanosomes(黑色素). The number, size and darkness of melanosomes per pigment cell determines skin colour.

It appears that, like the golden zebrafish, light-skinned Europeans also have a mutation(变异) in the gene for melanosome production. This results in less pigmented skin.

However, Keith Cheng, leader of the research team, points out that the mutation is different in human and zebrafish genes.

Humans acquired dark skin in Africa about 1.5 million years ago to protect bodies from ultra-violet rays of the sun(太阳光紫外线), which can cause skin cancer.

But when modern humans leave Africa to live in northern latitudes, they need more sunlight on their skin to produce vitamin D. So the related gene changes, according to Cheng.

Asians have the same version of the gene as Africans, so they probably acquired their light skin through the action of some other gene that affects skin colour, said Cheng.

The new discovery could lead to medical treatments for skin cancer. It also could lead to research into ways to change skin colour without damaging it like chemical treatment did on Michael Jackson.

The passage mainly tells us that ________.

A. people can not change their skin colour without any pain

B. the new discovery could lead to search into ways to change skin colour safely

C. pop king Michael Jackson often changed his skin colour as he liked

D. scientists have found out that people’s skin colour is determined by the gene

It can be inferred from the passage that ________.

A. nowadays people who want to change their skin colour have to suffer a lot from the damage caused by the chemical treatment

B. Europeans and Africans have the same gene

C. the new discovery could help to find medical treatments for skin cancer

D. there are two kinds of genes

Scientists have done an experiment on a dark-striped zebra fish in order to ________.

A. find the different genes of humans’

B. prove the humans’ skin colour is determined by the pigment gene

C. find out the reason why the Africans’ skin colour is dark

D. find out the ways of changing peopl’s skin colour

The writer’s attitude towards the discovery is ________.

A. neutral B. negative C. positive D. indifferent

Can people change their skin colour without suffering like pop king Michael Jackson? Perhaps yes. Scientists have found the gene that determines skin colour.

It appears that, like the golden zebrafish, light-skinned Europeans also have a mutation(变异) in the gene for melanosome production. This results in less pigmented skin.

However, Keith Cheng, leader of the research team, points out that the mutation is different in human and zebrafish genes.

Humans acquired dark skin in Africa about 1.5 million years ago to protect bodies from ultra-violet rays of the sun(太阳光紫外线), which can cause skin cancer.But when modern humans leave Africa to live in northern latitudes, they need more sunlight on their skin to produce vitamin D. So the related gene changes, according to Cheng.Asians have the same version of the gene as Africans, so they probably acquired their light skin through the action of some other gene that affects skin colour, said Cheng.

The new discovery could lead to medical treatments for skin cancer. It also could lead to research into ways to change skin colour without damaging it like chemical treatment did on Michael Jackson.

The passage mainly tells us that ________.

A. people can not change their skin colour without any pain

B. the new discovery could lead to search into ways to change skin colour safely

C. pop king Michael Jackson often changed his skin colour as he liked

D. scientists have found out that people’s skin colour is determined by the gene

It can be inferred from the passage that ________.

A. nowadays people who want to change their skin colour have to suffer a lot from the damage caused by the chemical treatment B. Europeans and Africans have the same gene

C. the new discovery could help to find medical treatments for skin cancer D. there are two kinds of genes

Scientists have done an experiment on a dark-striped zebra fish in order to ________.

A. find the different genes of humans’

B. prove the humans’ skin colour is determined by the pigment gene

C. find out the reason why the Africans’ skin colour is dark D. find out the ways of changing peopl’s skin colour

The reason why Europeans are light-skinned is probably that ________.

A. they are born light-skinned people

B. light-skinned Europeans have mutation in the gen for melanosome production

C. they have fewer activities outside D. they pay much attention to protecting their skin

The writer’s attitude towards the discovery is ________.

A. neutral B. negative C. positive D. indifferent

Can people change their skin colour without suffering like pop king Michael Jackson? Perhaps yes. Scientists have found the gene that determines skin colour.

It appears that, like the golden zebrafish, light-skinned Europeans also have a mutation(变异) in the gene for melanosome production. This results in less pigmented skin.

However, Keith Cheng, leader of the research team, points out that the mutation is different in human and zebrafish genes.

Humans acquired dark skin in Africa about 1.5 million years ago to protect bodies from ultra-violet rays of the sun(太阳光紫外线), which can cause skin cancer.

But when modern humans leave Africa to live in northern latitudes, they need more sunlight on their skin to produce vitamin D. So the related gene changes, according to Cheng.

Asians have the same version of the gene as Africans, so they probably acquired their light skin through the action of some other gene that affects skin colour, said Cheng.

The new discovery could lead to medical treatments for skin cancer. It also could lead to research into ways to change skin colour without damaging it like chemical treatment did on Michael Jackson.

51. The passage mainly tells us that ________.

A. people can not change their skin colour without any pain

B. the new discovery could lead to search into ways to change skin colour safely

C. pop king Michael Jackson often changed his skin colour as he liked

D. scientists have found out that people’s skin colour is determined by the gene

52. It can be inferred from the passage that ________.

A. nowadays people who want to change their skin colour have to suffer a lot from the damage caused by the chemical treatment

B. Europeans and Africans have the same gene

C. the new discovery could help to find medical treatments for skin cancer

D. there are two kinds of genes

53. Scientists have done an experiment on a dark-striped zebra fish in order to ________.

A. find the different genes of humans’

B. prove the humans’ skin colour is determined by the pigment gene

C. find out the reason why the Africans’ skin colour is dark

D. find out the ways of changing peopl’s skin colour

54. The reason why Europeans are light-skinned is probably that ________.

A. they are born light-skinned people

B. light-skinned Europeans have mutation in the gen for melanosome production

C. they have fewer activities outside

D. they pay much attention to protecting their skin

55. The writer’s attitude towards the discovery is ________.

A. neutral B. negative C. positive D. indifferent

Can people change their skin colour without suffering like pop king Michael Jackson? Perhaps yes. Scientists have found the gene that determines skin colour.

It appears that, like the golden zebrafish, light-skinned Europeans also have a mutation(变异) in the gene for melanosome production. This results in less pigmented skin.

However, Keith Cheng, leader of the research team, points out that the mutation is dif ferent in human and zebrafish genes.

Humans acquired dark skin in Africa about 1.5 million years ago to protect bodies from ultra-violet rays of the sun(太阳光紫外线), which can cause skin cancer.

But when modern humans leave Africa to live in northern latitudes, they need more sunlight on their skin to produce vit amin D. So the related gene changes, according to Cheng.

Asians have the same version of the gene as Africans, so they pr obably acquired their light skin through the action of some other gene that affects skin colour, said Cheng.

The new discovery could lead to medical treatments for skin cancer. It also could lead to research into ways to change skin colour without damaging it like chemical treatment did on Michael Jackson.

1.. The passage mainly tells us that ________.

A. people can not change their skin colour without any pain

B. the new discovery could lead to search into ways to change skin colour safely

C. pop king Michael Jackson often changed his skin colour as he liked

D. scientists have found out that people’s skin colour is determined by the gene

2.. Scientists have done an experiment on a dark-striped zebra fish in order to ________.

A. find the different genes of humans’

B. prove the humans’ skin colour is determined by the pigment gene

C. find out the reason why the Africans’ skin colour is dark

D. find out the ways of changing peopl’s skin colour

3.. The reason why Europeans are light-skinned is probably that ________.

A. they are born light-skinned people