单选题 Why do the treatment programs designed to change Type A behaviors face difficulties?

A、 Because the treatment programs are too expensive.
B、 Because the treatment programs consume too much time.
C、 Because it is unclear which aspect of the behavior of Type A leads to heart problems.
D、 Because the subjects are unwilling to receive this' kind of treatment.

【正确答案】 C

【答案解析】根据第四段所述目前这种治疗方法遇到困难是因为人们还不清楚，是A血型人的行为的哪方面引起心脏疾患。是由其中一种行为引起的，还是几种行为综合引起的，或是全部行为都能引起，还不清楚。[A]和[B]是目前这种治疗方法的现状。[D]文章未提及。