题目内容：

Two thirds of cancers are unavoidable even if you live a healthy life, a study has shown.

Scientists in the US found cancers are caused by random mistakes in the genetic code that occur when cells divide. The findings challenge the widespread view that cancer mutations are generally inherited or caused by environmental factors.

Lead scientist Dr. Cristian Tomasetti, from Johns Hopkins Kimmel Cancer Center in the US, said, “It is well-known that we must avoid environmental factors such as smoking to decrease our risk of getting cancer. But it is not as well-known that each time a normal cell divides and copies its DNA to produce two new cells, it makes various mistakes.”

The research, published in the journal Science, indicates that almost two-thirds of cancer-causing mutations are due to DNA copying errors. Overall, 66% of cancer mutations resulted from copying errors, 29% from lifestyle or environmental factors, and just 5% from inherited faulty genes. The discovery helps explains why cancer often strikes people who follow all the rules of healthy living and have no family history of the disease. Cancers caused by copying errors could occur no matter how perfect the environment is.

Professor Mel Greaves, director of the Centre for Evolution and Cancer at the Institute of Cancer Research in London, said, “Even if, as this study suggests, most individual cancer mutations are due to random chance, the researchers admit that the cancers they cause may still be preventable.”

“We have good evidence to show that cancer is caused by a complex mix of environmental exposures, inherited risk, and random chance. And while the genes we inherit from our parents are unchanged and many chance events are unavoidable, fortunately for us, exposures are major contributors to our risk of cancer and offer a route to risk reduction or prevention.”

1.What mainly causes cancers in the original belief?

A. Cancers are caused by random mistakes in the genetic code.

B. Cancers are usually caused by inheritance or environmental factors.

C. Cancers are usually caused by poisonous food.

D. It is undiscovered how cancers occur.

2.Which of the following is consistent with the passage?

A. Most people know that when a normal cell divides, it makes many errors.

B. As long as the environment is beneficial, people needn’t be concerned about cancers.

C. People with a healthy lifestyle won’t get cancers.

D. DNA copying errors are chiefly to blame for cancer mutations.

3.From Greaves’s words, which of the following is acceptable?

A. The cancers caused by copying errors may be avoidable.

B. We need change the genes that we inherit form our parents.

C. Cancers are caused by some single factor.

D. We have to accept the fact that cancers will be incurable.

4.Which section may the text belong to in a newspaper?

A. Environment.    B. Humanities.    C. Discovery    D. Technology.