When is bedtime? 【小题1】 Inside every living thing is a clock that follows the sun.

For a long time, people assumed that daylight told animals when to go to sleep or wake up. See light, wake. See dark, sleep. Then, in 1729, a French scientist named Jean-Jacques d’Ortous de Mairan did an experiment with a mimosa (含羞草), a plant that folds up its leaves at night. 【小题2】

From time to time, he peeked inside. To his surprise, the leaves continued to open and close each day as usual, even in total darkness. And he had discovered a new thing about living creatures. Inside every cell, there is a tiny clock that keeps track of whether it’s morning, noon, or night on the 24-hour cycle of a day. 【小题3】

Every cell in the body has its own tiny time-clicker. A master timekeeper in the brain keeps all these cell clocks in step. For humans, a small group of cells at the back of the eye are in charge of the special job. 【小题4】 The master clock then sends “wake up” or “sleep” chemicals to all your cells.

You can feel light reset your clock if you fly to a different time zone. For a few days you get sleepy at bedtime back home even if it’s afternoon in your new place. This is called “jet lag”. 【小题5】 But soon the bright light in the morning and dark at night will reset your master clock to match the local time where you are, and you’re back on schedule.

So don’t worry if you forget your watch—your clock inside will keep you on sun time.

There is an English saying:“ laughter is the best medicine.” Until recently, few people took the saying seriously. Now, however, doctors have begun to look into laughter and the effects it has on the human body. They have found that laughter really can improve people’s health.

Tests were carried out to study the effects of laughter on the body. People watched funny films while doctors checked their hearts, blood pressure, breathing and muscles. It was found that laughter had similar effects to physical exercise. It increases blood pressure, the heart beating and breathing; it also works several groups of muscles in the face, the stomach, and even the feet. If laughter exercises the body, it must be beneficial .

Other tests have shown that laughter appears to be able to reduce the effect of pain on the body. In one experiment doctors produced pain in groups of students who listened to different radio programs. The group that tolerated(忍耐)the pain for the longest time was the groups which listened to a funny program. The reason why laughter can reduce pain seems to be that it helps to produce a kind of chemicals in the brain which diminish both stress and pain.

As a result of these discoveries, some doctors in the United States now hold laughter clinics, in which they help to improve their patients’ condition by encouraging them to laugh. They have found that even if their patients do not really feel like laughing, making them smile is enough to produce beneficial effects similar to those caused by laughter.

Immigrant children are often highly motivated and have ambitious parents. And these clever, knowledge-hungry youngsters often achieve higher results than the rest of the classmates.

In 1954, the United States opened its borders to an immigrant from Syria. His son, Steve Jobs, became one of the most creative entrepreneurs（企业家）.In the current refugee crisis, that might look like a fairy tale, but it is not that unbelievable.

While immigrant youngsters might face cultural, social and economic disadvantages, the top 10% of 15- year-old students with an immigrant background in the United States did just as well as the top 10% without an immigrant background, as measured by Pisa, an international test.

In fact, when considering social background, these high-achieving immigrant teenagers were almost a school year ahead.

This doesn't only happen in the United States. In 13out of the 37 countries with comparable data, including the United Kingdom, the top 10% of immigrants were at least 10 points ahead of the non-immigrant students in Pisa, after considering social background.

These highly motivated students, managing to overcome the double disadvantages of poverty and an immigrant background, have the potential（潜力）to make exceptional contributions to their host countries.

On average across all countries, top performing immigrants and non-immigrants reached similar levels of performance on the Pisa mathematics test. Many immigrants seem determined to make the most of any opportunity that arises. Their children also seem ready to take on an academic challenge. Alongside the Pisa are questions about students' willingness to try to solve more complex problems. First-generation immigrants, including in the UK, are more likely than average to want to stretch themselves and try to answer more difficult problems.

The OECD's research shows that in most cases immigrant students and their parents hold an ambition to win the matches, and in some cases they go beyond the expectations of families in their host country. For example, parents of immigrant students in Belgium, Germany and Hungary are more likely to expect that their children will go to university and get a degree than parents of students without an immigrant background.