XDF兰书精选题中两道想不明白的结论题，求助

18.Although aspirin has been proven to eliminate moderate fever associated with some illnesses, many doctors no longer routinely recommend its use for this purpose. A moderate fever stimulates the activity of the body's disease-fighting withe blood cells and also inhibits the growth of many strains of disease-causing bacteria.

If the statements above are true, which of the following conclusions is most strongly supported by them?

B.Aspirin can prolong a patient's illness by eliminating moderate fever helpful in fighting some diseases.

C.Aspirin inhibits the growth of white blood cells, which are necessary for fighting some illnesses.

谁能帮我解释下为什么B对而C错吗？

19.Roland: The alarming fact is that 90percent of the people in this country now report that they know someone who is unemployed.

Sharon: But a normal, moderate  level of unemployment is 5 percent, with 1 out of 20workers unemployed. So at any given time if a person knows approximately 50 workers, 1 or more will very likely be  unemployed.

Sharon's argument is structured to lead to which of the following as a conclusion?

A. The fact that 90% of the people know someone who is unemployed is not an indication that unemployment is abnormanlly high.

C. If at least 5% of workers are unemplyed, the result of questioning a representative group of people cannot be the percentage Roland cites.

想知道为什么A对，而C错。

18,是不是说：growth of WBC与activity of WBC不一样

19，5%只是失业率，跟认识失业者的人在全体人中的比例没有必然联系吧