2. Crimes are mainly committed by the young, and for this reason merely increasing the number of police officers or expenditures on police services has little effect on reducing the crime rate. In fact, the only factor associated with a crime-rate drop is a decrease in the number of people in the community aged fourteen to thirty.

The findings above can best serve as part of an argument against

(A) the likelihood that any law enforcement program will be effective in reducing the crime rate within a short time

(B) increasing prison terms for young people found guilty of crimes

(C) introducing compulsory military conscription for people aged seventeen to nineteen

(D) raising the age at which students are permitted to leave school（A）

(E) a community’s plan to increase the number of recreational and educational activities in which young adults can participate

我想问一下，这个题目的答案为什么是A？A好像跟题干所说的青少年的数目没有关系啊。我选的E为什么不对？

另外，我还搞不清楚的是，这里问的是argument against，应该怎么理解？还有的题目是说weaken argument，跟weaken conclusion有什么区别？有的题目前面先说一个结论，后面的一句话是前面的结论的解释或原因，那么是否后面的是argument前面的是conclusion？