题目内容：

A medical study has shown that excess(过度的)coffee drinking could cause heart attacks in people who do not metabolize(使新陈代谢)caffeine fast enough.

The study, published recently in the Journal of the American Medical Association, says an enzyme(酶)that metabolizes caffeine in the liver works differently in some people, depending on the make­up of the gene(基因). People who have a slow version (版本)of the enzyme are at a greater risk(风险)of a heart attack when they drink more coffee. The risk had something to do with a person's age and how many cups of coffee he drinks.

The team from the University of Toronto in Canada studied 4,024 people living in coffee­rich Costa Rica between 1994 and 2004, of whom half suffered non­fatal(非致命的)heart attacks. They found slightly more than half had the slow version of the gene, while the rest had the fast form.

Two to three cups of coffee a day increased the possibilities of a heart attack by 36 percent for those with the slow­acting gene and four or more cups a day lifted it by 64 percent.

But those under 50 who had the fast version of the gene had a lower risk of heart disease, even with four or more cups a day.

Those with the fast­acting gene who drank two to three cups of coffee a day had 22 percent reduced possibilities of having a heart attack, but drinking four or more cups a day only lessened the risk by 1 percent. Scientists recommend limiting coffee consumption(消耗量)to within four cups a day.

1.People who have a slow version of the enzyme________.

A. are in danger when they drink coffee    B. are living in coffee­rich Costa Rica

C. have the slow version of the gene    D. can not drink four or more cups of coffee a day

2.The example of Costa Rica the author presented in the passage proves that________

A. the heart attack in Costa Rica is really serious.

B. the heart problem has something to do with drinking coffee.

C. people in Costa Rica cannot metabolize caffeine in the liver.

D. more than half people have the slow version of gene.

3.It can be concluded that the passage is most probably written for________

A. doctors who study heart disease

B. specialists who offer medical care

C. old people who have the slow version of the gene

D. those who love drinking coffee every day

4.What is the best title for this passage?

A. Coffee and heart attacks    B. Gene and heart disease

C. Caffeine and enzyme    D. Reasons for heart problems