Below is a selection from a popular science book.
If blood is red, why are veins（静脉） blue?
Actually, veins are not blue at all. They are more of a clear, yellowish color. Although blood looks red when it’s outside the body, when it’s sitting in the vein near the surface of the skin, it’s more of a dark reddish purple color. At the right depth, these blood-filled veins reflect less red light than the surrounding skin, making them look blue by comparison.
Which works harder, you heart or your brain?
That kind of depends on whether you’re busy thinking or busy exercising. Your heart works up to three times harder during exercise, and shifts enough blood over a lifetime to fill a supertanker. But in the long run, your brain probably tips it, because even when you’re sitting still your brain is using twice as much energy as your heart, and it takes four to five times as much blood to feed it.
Why do teeth fall out, and why don’t they grow back in grown-ups?
Baby (or “milk”) teeth do not last long; they fall out to make bigger room for bigger, stronger adult teeth later on. Adult teeth fall our when they become damaged, decayed and infected by bacteria. Once this second set of teeth has grown in, you’re done. When they’re gone, they are gone. This is because nature figures you’re set for life, and what controls regrowth of your teeth switches off.
Do old people shrink as they age?
Yes and no. Many people do get shorter as they age. But, when they do, it isn’t because they’re shrinking all over. They lose height as their spine（脊柱） becomes shorter and more curved due to disuse and the effect of gravity(重力). Many (but not all) men and women do lose height as they get older. Men lose and average of 3-4 cm in height as they age, while women may lose 5 cm or more. If you live to be 200 years old, would you keep shrinking till you were, like 60 cm tall, like a little boy again? No, because old people don’t really shrink! It is not that they are growing backwards ----- their legs, arms and backbones getting shorter. When they do get shorter, it’s because the spine has shortened a little. Or, more often, become more bent and curved.
Why does spinning make you dizzy（眩晕的）?
Because your brain gets confused between what you’re seeing and what you’re feeling. The brain senses that you’re spinning using special gravity-and-motion-sensing organs in your inner ear, which work together with your eyes to keep your vision balance stable. But when you suddenly stop spinning the system goes out of control, and your brain thinks you’removing while you’re not.
Where do feelings and emotions come from?
Mostly from an ancient part of the brain called the limbic system. All mammals have this brain area ----- from mice to dogs, cats, and humans. So all mammals feel basic emotions like fear, pain and pleasure. But since human feelings also involve other, newer bits of the brain, we feel more complex emotions than any other animal on this planet.
If exercise wears you out, how can it be good for you?
Because our bodies adapt to everything we do to them. And as far as your body is concerned, it’s “use it, or lose it”! It’s not that exercise makes you healthy, it’s more that a lack of exercise leaves your body weak and easily affected by disease
【小题1】What is the color of blood in a vein near the surface of the skin?

Below is a selection from a popular science book.

If blood is red, why are veins（静脉） blue?

Actually, veins are not blue at all. They are more of a clear, yellowish color. Although blood looks red when it’s outside the body, when it’s sitting in the vein near the surface of the skin, it’s more of a dark reddish purple color. At the right depth, these blood-filled veins reflect less red light than the surrounding skin, making them look blue by comparison.

Which works harder, you heart or your brain?

That kind of depends on whether you’re busy thinking or busy exercising. Your heart works up to three times harder during exercise, and shifts enough blood over a lifetime to fill a supertanker. But in the long run, your brain probably tips it, because even when you’re sitting still your brain is using twice as much energy as your heart, and it takes four to five times as much blood to feed it.

Why do teeth fall out, and why don’t they grow back in grown-ups?

Baby (or “milk”) teeth do not last long; they fall out to make bigger room for bigger, stronger adult teeth later on. Adult teeth fall our when they become damaged, decayed and infected by bacteria. Once this second set of teeth has grown in, you’re done. When they’re gone, they are gone. This is because nature figures you’re set for life, and what controls regrowth of your teeth switches off.

Do old people shrink as they age?

Yes and no. Many people do get shorter as they age. But, when they do, it isn’t because they’re shrinking all over. They lose height as their spine（脊柱） becomes shorter and more curved due to disuse and the effect of gravity(重力). Many (but not all) men and women do lose height as they get older. Men lose and average of 3-4 cm in height as they age, while women may lose 5 cm or more. If you live to be 200 years old, would you keep shrinking till you were, like 60 cm tall, like a little boy again? No, because old people don’t really shrink! It is not that they are growing backwards ----- their legs, arms and backbones getting shorter. When they do get shorter, it’s because the spine has shortened a little. Or, more often, become more bent and curved.

Why does spinning make you dizzy（眩晕的）?

Because your brain gets confused between what you’re seeing and what you’re feeling. The brain senses that you’re spinning using special gravity-and-motion-sensing organs in your inner ear, which work together with your eyes to keep your vision balance stable. But when you suddenly stop spinning the system goes out of control, and your brain thinks you’removing while you’re not.

Where do feelings and emotions come from?

Mostly from an ancient part of the brain called the limbic system. All mammals have this brain area ----- from mice to dogs, cats, and humans. So all mammals feel basic emotions like fear, pain and pleasure. But since human feelings also involve other, newer bits of the brain, we feel more complex emotions than any other animal on this planet.

If exercise wears you out, how can it be good for you?

Because our bodies adapt to everything we do to them. And as far as your body is concerned, it’s “use it, or lose it”! It’s not that exercise makes you healthy, it’s more that a lack of exercise leaves your body weak and easily affected by disease

1.What is the color of blood in a vein near the surface of the skin?

A．Blue                                 B．Light yellow

C．Red                                  D．Dark reddish purple

2.Why do some old people look a little shrunken as they age?

A．Because their spine is in active use.

B．Because they are more easily affected by gravity.

C．Because they keep growing backwards.

D．Because their spine becomes more bent.

3.Which of the following statements about our brain is true?

A．In the long run, our brain probably works harder than our heart.

B．When our brain senses the spinning, we will feel dizzy.

C．The brains of the other mammals are as complex as those of humans.

D．Our feelings and emotions come from the most developed area in our brain.

4.What is the main purpose of the selection?

A．To give advice on how to stay healthy.

B．To provide information about our body.

C．To challenge new findings in medical research.

D．To report the latest discoveries in medical science.

One day, a teacher was speaking to a group of students about how to manage time. He gave such an interesting example that his students would never   26  .

He put a wide-mouth jar(罐) on the table. Then he    27  some rocks and carefully placed them into the jar, one at a time. When   28  rocks would fit inside, he   29  , “Is this jar full?”

Everyone in class shouted, “Yes.” “Really?” The teacher pulled out a bag of small stones. He put   30  small stones in and shook the jar. The small stones went   31  into the spaces between the big rocks. He then asked the group   32  , “Is this jar full?”

“Probably not,” one of them answered. “Good!” the teacher replied. He brought out a box of sand and   33  some sand on the jar and it went between the rocks and small stones. Again he asked the   34  question, “Is this jar full?

“No,” the class shouted. Once more the teacher said, “Good.” He poured a cup of water into the jar   35  it was full. The he asked, “What is the point here?” One student   36  his hand and said, “The point is that if you try really hard, you can   37  put more things in.”

“No,” the teacher replied, “that’s not the   38  . What I want to tell you is that if you don’t put the big rocks in first, you will never get others in at all.   39  are the ‘big rocks’ in your life? Time with your friends, your education or your dreams? Remember to put the   40  in first, or you’ll never get others in at all?”

1.                A．remember      B．like            C．forget    D．think

2.                A．handed out      B．took out        C．carried away   D．put away

3.                A．no more        B．not more        C．no many  D．not many

4.                A．answered       B．read           C．asked    D．said

5.                A．no            B．few            C．any  D．some

6.                A．up            B．out            C．down D．away

7.                A．no more        B．once again      C．a third time    D．a fourth time

8.                A．sent           B．put            C．bought   D．collected

9.                A．same          B．different        C．difficult   D．common

10.               A．since          B．till             C．while D．because

11.               A．offered        B．placed         C．raised D．shook

12.               A．always         B．already         C．never D．hardly

13.               A．point          B．example        C．promise   D．story

14.               A．When          B．What          C．Who  D．Why

15.               A．sand           B．small stones     C．big rocks  D．water