题目内容：

As an expert on the science of sleep and sleep disorders, Michael Twery believes “People have good understanding about the necessity of sleeping 7-8 hours in bed. But they undervalue the function of napping in day.”

For example, many Americans do nap. But one-third of adults in the US are also frequently tired. Someone who naps as a way of paying off a sleep debt may not experience the same improvements from napping as a healthy, well-rested person would.

Also, many people may not want to admit that they take a nap. That only children, the very old, sick or lazy people nap is a common opinion. In fact, Americans sometimes do very strange things. For those who claim they only sleep five hours a night, they may think they are somehow stronger than the average human—superhuman, if you will.

Luckily, many offices now offer napping rooms in many U. S. cities. While resting in the middle of the work day may seem like a luxury to Americans, napping is very much part of a normal, everyday life in other parts of the world.

China, generally speaking, is a land of nappers. Researchers recently looked at information provided by nearly 3, 000 Chinese adults, aged 65 years or older. Based on their answers, researchers put them into four groups: non-nappers (0 minutes), short nappers (less than 30 minutes), moderate nappers (30-90minutes), and extended nappers (more than 90 minutes).

The study found that the hour-long nappers did better on the tests than those who napped for shorter and longer periods. Keep in mind, however, that these are the findings for those over the age of 65.

Michael Twery notes that an hour long nap may be too long for young, healthy adults. “Currently, 30 minutes is enough to remove the pressure to sleep and will help us feel more awake. If we nap longer, we will get trapped into sleep inertia—a very deep sleep period.”

1.What does Michael Twery mean in the first paragraph?

A. Most people have a sleep for a proper time.

B. Most people have a good understanding of napping.

C. Sleeping at night is more important than napping in day.

D. People should learn more about the benefits of napping.

2.According to the underlined sentence, many Americans think taking a nap is ________.

A. useless

B. shameful

C. enjoyable

D. necessary

3.According to the study in China, which of the following is true?

A. Old people are less likely to be short nappers.

B. The research did not cover findings for young people.

C. People are advised to nap for more than an hour per day.

D. Those who take part in the study are divided into three groups.

4.What is the passage mainly about?

A. We can get negative results from sleep inertia.

B. Americans are unwilling to admit their habit of napping.

C. The longer you nap, the healthier you get.

D. A proper amount of nap is essential for better health.