Sunshine does make people happier. Imagine how cheerful you are when it clears up after long cold rainy days. Let’s discover science behind sunlight.

Sunlight causes you to produce a chemical (化学物质) called serotonin (血清素). When you are exposed to sunlight, your body will make more serotonin. Higher levels of serotonin will keep you in good spirits. At night, when there is little or no light, your body produces another chemical-melatonin (褪黑激素). It helps your body relax and will make you feel tired, which can prepare you for a good night’s sleep. You should keep a good balance between these two chemicals.

However, for many people, it is hard to balance sunlight with darkness. People who stay indoors a lot may not get enough sunlight. The light in a house is usually about 100 times less than that outside on a sunny day. That’s why it is believed that those people should get outside in the sunshine. They can get some exercise, enjoy the fresh air and be happy, all at the same time.

There are places where it gets dark for a long time in the winter. People in those places are easier to get seasonal affective disorder (SAD). People with SAD usually go through bad experiences such as low energy and sadness. The most common treatment for those people is to sit under bright artificial (人工的) lights for some time.

The roles that sunshine plays in people’s life are more than those above. For example, your body produces Vitamin D (维生素D) from sunlight, which is important for being healthy. In fact, there is more science about sunlight for you to discover. So next time, when you notice the sunshine on your shoulder, take a moment to think, “Why do we love sunshine?”

1. 1．Which of the following can take the place of “are exposed to” in the text?

A    stay in

B    care about

C    dream of

D    depend on

2. 2．What does Paragraph 2 mainly talk about?

A    What can help people to keep in good spirits

B    How light influences people through chemicals.

C    Why melatonin can help people relax for a sleep.

D    Which chemical is thought to be more important.

3. 3．Which of the following is an opinion (观点) according to the text?

A    There are places where it gets dark for a long time in the winter.

B    People who stay indoors a lot should get outside in the sunshine.

C    The light in a house is usually less than that outside on a sunny day.

D    People’s bodies produce something called Vitamin D from sunlight.

4. 4．Jack is a person with SAD. How could he solve his problem according to the text?

A    By staying indoors a lot.

B    By taking in more fresh air.

C    By doing some exercise.

D    By using man-made lights

5. 5．Why is the sentence “Why do we love sunshine?” written in the last paragraph?

A    To encourage readers to learn more about sunlight.

B    To advise readers to stay in houses for enough time.

C    To expect readers to realize the importance of Vitamin

D    To invite readers to walk into nature to enjoy the fresh air.