174. In 1987 sinusitis was the most common chronic medical condition in the United States, followed by arthritis and high blood pressure, in that order. The incidence rates for both arthritis and high blood pressure increase with age, but the incidence rate for sinusitis is the same for people of all ages. The average age of the United States population will increase between 1987 and 2000. Which of the following conclusions can be most properly drawn about chronic medical conditions in the United States from the information given above? (A) Sinusitis will be more common than either arthritis or high blood pressure in 2000. (B) Arthritis will be the most common chronic medical condition in 2000. (C) The average age of people suffering from sinusitis will increase between 1987 and 2000. (D) Fewer people will suffer from sinusitis in 2000 than suffered from it in 1987. (E) A majority of the population will suffer from at least one of the medical conditions mentioned above by the year 2000.

这到底的推理过程是什么呀？请大家说说，我怎么也没想明白！谢谢！！

C? 对吗？．

得S病的人不会在老年人群中迅速增加，但是总的人群变老，所以得S病的人平均年龄变老.

只能排除呀！我觉得是这样，这种病与年龄无关，所以不会在年轻人中间流行，而且这是慢性病，当初得病的那些人不会被治愈，而且总体的病人数没有大的波动，随着这些得病的人的年龄增长，得这种病的人的平均年龄也增长。如果按2楼的说法说不通，因为如果在老年人中增加的话，平均年龄也会增长。不在老年人中增加而在年轻人中增加的话，平均年龄就下降。我觉得这提出的不严谨！

因为：各年龄段得s的几率相等

所以：得s病的平均年龄就是整个米国的平均年龄

又因为：米国人口老化平均年龄上升

所以：得s病的人的平均年龄上升