When people lose legs after accidents or illnesses, emergency care and artificial limbsoften allow them to walk again. Newts in the same situation, on the other hand, can grow limbs back on their own! 题目和参考答案——青夏教育精英家教网—

题目内容

When people lose legs after accidents or illnesses, emergency care and artificial limbs（假肢）often allow them to walk again. Newts （蝾螈） in the same situation, on the other hand, can grow limbs back on their own! Scientists have known for a long time that certain animals can re–grow limbs, but they haven’t quite figured out how these creatures do it.

Researchers have now come up with some new ideas. Their work may give people the ability to re – grow lost limbs. The researchers started with two simple experiments：when you cut a newt’s leg at the ankle, only the foot grows back；when you cut off a leg at the very end, the whole leg grows back. In both cases, the re–growth begins with stem cells. Stem cells can develop into nearly any type of cell in the body.

How do a newt’s stem cells know when to grow only a foot and when to re–grow a whole leg?

This question relates to another mystery. In newts, a cut–off leg will grow back only if the nerve bundle（神经束）in it also grows back , but if something prevents the nerve bundle from growing, the stem cells at the wound won’t re–grow a new leg.

In its study, a British team focused on a protein called nAG. When the team prevented nerves in a limb from growing, but added the nAG protein to stem cells in the limb, the limb still re–grew. That protein seems to guide limb re–growth. People have proteins that are similar to nAG. Further research into these materials may someday help human limbs recover by themselves.

1．In the experiments, the researchers cut off a newt’s foot or leg to find out _____.

A．what stem cells were B．whether they would grow back

C．how long it would take to re–grow D．how they would re – grow

2．A newt will re–grow its leg if _____.

A．its ankle was cut off but the nerve bundle was good

B．its leg was cut off and the nerve bundle stopped growing

C．its leg was cut off and the nerve bundle could grow back

D．its ankle and the nerve bundle were cut off

3．What do the underlined words “these materials” refer to?

A．Nerve bundles and proteins. B．Proteins similar to nAG.

C．Stem cells and proteins. D．Stem cells and nerve bundles.

4．The first sentence of the passage _____.

A．acts as a lead–in B．shows where researchers got their new ideas

C．states the author’s opinion D．describes the result of researchers’ studies

DCBA

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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.

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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

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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

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

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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.

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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