You may have heard adults say they are uncomfortable in the morning without a cup of coffee. One reason they may feel that way is that coffee contains caffeine（咖啡因）. Caffeine occurs naturally in coffee, tea, and cocoa beans, which are used to make chocolate. But now food makers are adding it to many products, from potato chips to water.
The US government is especially worried about the problem. That's why the Food and Drug Administration （FDA） is studying the health effects of caffeine on young people. Studies show that too much caffeine can make people nervous and unable to sleep. What's more, caffeine is habit-forming. Those who consume it regularly and stop suddenly may experience headaches and feel tired.
One of the biggest concerns is the large amount of caffeine added to so-called energy drinks, like Red Bull. A 12-ounce can of cola has about 35 milligrams of caffeine. A similar serving of Red Bull contains more than three times that amount.
The Institute of Medicine is also working on caffeine-safety measures. "Teenagers should not drink beverages that contain caffeine. They should be aware of caffeine's effects on health and on how the brain works. Take, for example, teenagers who consume caffeine to stay awake and study for a test. They will remember less of what they just studied," said Stallings, a member of the institute.
Companies that make products with added caffeine claim they do not advertise them to kids. However, there is no law to stop children from buying them. So the FDA needs to set limits on caffeine, especially in energy drinks. As for added caffeine in foods, the government should just say no. If not, the amount of caffeine should be printed on food labels to remind consumers. The government must do that.
Doctors say kids should avoid caffeine. If you need extra energy, try these natural boosters：eat right, exercise, and get plenty of sleep.
What is the US government particularly concerned about？ ______
A. The fact that coffee contains caffeine.
B. The practice of adding caffeine to foods.
C. The measures of avoiding caffeine's effects.
D. The practice of using caffeine to make chocolate.
Red Bull is listed in the third paragraph as an example of ______ .
A. caffeine's effects on health
B. teenagers' addiction to caffeine
C. drinks which contain much caffeine
D. people's concern about teenagers' health
Paragraph 5 is mainly about ______ .
A. the measures of protecting teenagers from caffeine's effects
B. the process of the government's controlling the use of caffeine
C. the government's responsibility of taking care of teenagers
D. the risk of buying products containing caffeine nowadays
The author may agree that ______ .
A. headaches and feeling tired are common in teenagers
B. food makers don't add much caffeine to many products now
C. caffeine is good and useful for teenagers' study
D. getting enough sleep can make people energetic
