one lr question

high school students who feel that they are not succeeding in school often drop out before graduating and go to work. last year, however, the city's high school dropout rate was significant lower than the previous year's rate. this is encouraging videmce that the program instituted two yaers ago to improve the morale of high school students has begun to take effect to reduce dropouts.

which one of the following, if true about the last year, most seriously weakens the argument?

a there was a recession that caused a high level of unemployment in the city.

c as in the previous year, more high schoool students remained in school than dropped out.

can someone telll me why a is right, but c is wrong????? thank u so much!!!

high school students who feel that they are not succeeding in school often drop out before graduating and go to work. last year, however, the city's high school dropout rate was significant lower than the previous year's rate. this is encouraging videmce that the program instituted two yaers ago to improve the morale of high school students has begun to take effect to reduce dropouts.

which one of the following, if true about the last year, most seriously weakens the argument?

a there was a recession that caused a high level of unemployment in the city.

c as in the previous year, more high schoool students remained in school than dropped out.

can someone telll me why a is right, but c is wrong????? thank u so much!!!

For my understanding, (a) offers an "alternative explanation" indicating that the "reduction of dropouts" may not due to the "program" but other reasons, which lessens the credibility of the conclusion, then weakens the argument.

Since the "program" was adopted "two years ago", if during the same time, according to (c), the rate of dropouts was already reduced, which actually may strengthen rather than weaken the argument.  

Feel free to drop your comments.Thanks!

which one of the following, if true about the last year, most seriously weakens the argument?

a there was a recession that caused a high level of unemployment in the city.

c as in the previous year, more high schoool students remained in school than dropped out.

显然，A是正确的选项。

可能楼主没有仔细看题，本题问的是 if true about the last year, most seriously weakens the argument?

Weaken的意思是“削弱”，而C答案是就事实的陈述，是对argument的“证明”，不具备“削弱”，而A答案的意思是用“他因”产生的“削弱”，即“因为去年工作不好找这个原因，所以学生的drop-out rate下降了”，用“工作不好找的他因”，消弱了“两年前成立的这个机构对rate下降的直接影响”，这当然是“削弱”啦！

综上，A是毫无争议的唯一答案。