A、More than 400. B、More than 4,000. C、About 200. D、About 50. C原文提及“400多人参与了这次研究．几乎半数患有高血压。”故C正确。

Most doctors have long believed that reducing salt can decrease blood pressure. A new American study suggests this is true even when people do not eat the healthiest foods.
    The research appeared in the New England Journal of Medicine. A team at Brigham and Women’s Hospital in Boston, Massachusetts performed the study. Frank Sacks of Harvard University Medical School led the team.
    More than four-hundred people took part in the research. Almost half of them had high blood pressure. They all ate foods with different amounts of salt. Salt contains sodium. There is strong evidence that sodium affects blood pressure.
    Half the people ate an average American diet. Their food was high in fat and cholesterol. The other people ate low-fat, low-cholesterol foods. Members of the low-fat group ate many vegetables, fruits and grains.
    The study showed that the people who ate healthful foods while eating less salt lowered their blood pressure the most. However, blood pressure decreased for both groups when they ate less salt. Almost fifty-million Americans have high blood pressure. Continued high-blood pressure is dangerous because it can increase the risk of heart disease and stroke.
    Philip Greenland of Northwestern University Medical School in Chicago, Illinois praised the study. He said the decreases in blood pressure among the people in the study were similar to those caused by medicine. However, Doctor Greenland said popular prepared foods need to be improved if people are to decrease salt in their diets. He said most people get their salt mainly from these prepared foods. They include many soups and cooked meat products.
9.Among  the participants in the research, how many of them have high blood pressure?
10.What does the study at Brigham and Women’s Hospital seem to prove?
11.What is mentioned as one of the causes of increasing the risk of heart disease?
12.What is the proposal presented by Doctor Greenland?