Rarely do major diseases have a single cau

题目：

Rarely do major diseases have a single cause. They are usually the result of a complex interaction between many factors, including genetic, environmental and lifestyle components. Many media reports, however, can tead us to believe that if we gave up something that we might otherwise enjoy, we could completely escape that particular affliction.

Clearly, this is not the case. Vegetarians die of cancer of the colon (结肠). Teetotallers die of liver complaints, including cirrhosis (硬化). People who never go out in the sun contract skin melanomas (黑素瘤). Always, there are other factors at work than the single element being examined in a scientific study.

Quite often the alleged benefits of a particular nutritional element are the result not so much of the element itself but of the lifestyle and general diet of the people who consume it most. People who eat lots of "healthy" foods, including fiber, carrots, broccoli etc. , also tend to drink less alcohol, take more exercise, avoid too many fatty foods and smoke less. Only when a study can rule out all of these other factors and often we do not know what these factors might be can we say that there is a causal link between two things. That is not to say that things like fiber and broccoli have no beneficial effects at all. But those with sedentary lifestyles cannot expect these foods to make them healthy.

There is, however, one thing which increases the likelihood of dying relatively young, even when all of the other factors have been taken into account. It is one of the biggest killers even among those who lead lifestyles which, by any criteria, are clearly healthy ones. This single, incontrovertible risk factor is that of being poor. Recent report from the Cancer Research Campaign suggested that 12 700 deaths could have been avoided between 1986 and 1990 if inequalities in cancer care did not exist in England and Wales. Comparing cancer survival rates, the study found that England and Wales fared unfavorably with Europe and the US, but the most affluent regions of these two countries exhibited similar figures to the European average.

In an attempt to counter this disparity the government has announced plans for the provision of Health Action Zones which seek to encourage greater cooperation between health and social services, targeting both rural and inner city areas. The emphasis of this new scheme however appears to focus on inadequacies within health education in these areas, rather than attacking the broader issues of social inequality.

According to the author, fiber and broccoli are the so-called "healthy" foods because（）

A. they are only part of a general diet and lifestyle that contribute to good health

B. the benefits of these foods are still unknown

C. the foods do not benefit people with sedentary lifestyles

D. people who eat these foods tend to adopt unhealthy lifestyles