题目内容：

    Astronauts traveling in space meet forms of radiation that are uncommon on Earth. Some of this radiation has been shown to be harmful to human health. It is linked to cancers and heart problems. Yet a new American study suggests the radiation does not shorten astronauts' lives.

Researchers studied nearly 60 years of health records and other data about male astronauts from the United States. They then compared this data with information about a group of men who are in good health, richer than most Americans and receive good health care-professional athletes. The study found that neither group has higher rates of dying at a young age. In fact, both groups generally live longer than other Americans.

Astronauts are usually well-educated, earn more money and are in better physical condition than the average American. Some earlier research has linked being an astronaut to a lower risk of early death, the researchers noted. The findings were reported in the publication Occupational & Environmental Medicine.

Much of the existing research on mortality rates in astronauts has not yet explored the mental and physical demands of this job. There also has not been a lot of research on whether astronauts show what is known as the "healthy worker effect". This effect leads people with employment of any kind to have fewer medical problems than people who are unable to work, said Robert Reynolds.

Reynolds said, "The challenge has always been to understand if astronauts are as healthy as they would be had they been otherwise comparably employed but had never gone to space at all. To do this, we need to find a group that is comparable on several important factors."

1.How did researchers carry out their study?

A.By doing interviews. B.By analyzing some factors.

C.By comparing different data. D.By doing experiments in the lab.

2.What can we learn from the text?

A.All radiation is harmful to human health.

B.Athletes tend to be poorer than most Americans.

C.Healthy worker effect makes working people healthier.

D.Research has explored the mental and physical demands of being astronauts.

3.What can he inferred from Reynolds' words?

A.They are determined to face the challenge.

B.The research is almost impossible to conduct.

C.Several important factors hold back the research.

D.Astronauts are as healthy even they haven't been Astronaut.

4.What can be a suitable title for the text?

A.Astronauts----Healthy or Otherwise

B.Astronauts Are as Healthy as Athletes

C.Radiation Affects Astronauts' Health

D.Astronauts---- Well-Educated and Earn More