
Passage: Researchers have found that eating more than five servings of yam, corn, carrots, onions or other similar vegetables a day can reduce the risk of pancreatic cancer. They surveyed 2230 respondents, including 532 patients with pancreatic cancer, then classified the agricultural products eaten by cancer patients and asked them about their other living habits, such as overall diet and smoking. Compare it with the living habits of the other 1701 people.It was found that people who ate at least five servings of vegetables a day were half as likely to develop pancreatic cancer as those who ate less than two servings of vegetables a day.
Question: Which of the following options is most helpful to prove the reliability of the above conclusions?
A. A.To find out the proportion of patients with pancreatic cancer in groups that are meat-based and rarely eat the vegetables mentioned above.
B. B.To study the clinical manifestations and treatment of the patients of developing pancreatic cancer .
C. C.Make the life of patients with pancreatic cancer as happy as possible to prolong their lives.
D. D.Through the study of the laboratory, to find out what ingredients are contained in the above-mentioned vegetables.
Answer: