单选题 Sound personal health choice is often difficult to make because

A、 current medical knowledge is still insufficient.
B、 there are many factors influencing our decisions.
C、 few people are willing to trade the quality of life for the quantity of life.
D、 people are usually influenced by the behavior of their friends.

【正确答案】 B

【答案解析】[解析] 本题考查细节。文章第一段末尾部分和第二段的开头部分是回答这一问题的依据。[B]与此相符，为正确答案。文章在说及对造成个人选择困难时举了一个比较明显的例子，然后说：因素是多种多样的，(a multitude of factors)有内在的因素(inherited factors)，也有外在环境的因素(environmental factors)．