求教lsat-9-1-13

liy_lilan

Five years ago, during the first North American outbreak of the cattle disease CXC, the death rate from the disease was 5 percent of all reported cases, whereas today the corresponding figure is over 18 percent. It is clear, therefore, that during these past 5 years, CXC has increased in virulence.

Which one of the following, if true, most substantially weakens the argument?

(A) Many recent cattle deaths that have actually been caused by CXC have been mistakenly attributed to another disease that mimics the symptoms of CXC.

(B) During the first North American outbreak of the disease, many of the deaths reported to have been caused by CXC were actually due to other causes.

(C) An inoculation program against CXC was recently begun after controlled studies showed inoculation to be 70 percent effective in preventing serious cases of the illness.

(D) Since the first outbreak, farmers have learned to treat mild cases of CXC and no longer report them to veterinarians or authorities.

(E) Cattle that have contracted and survived CXC rarely contract the disease a second time.

答案是D，但是我认为D不是削弱而是加强。因为既然有的CXC病例没有报告，那显然有比18%还高的比例染病，不正说明CXC泛滥成灾了吗？我倒认为A和B有可能是削弱呢。还请高人指点。

lawyer_1

这是计算基数的问题,基数小,百分比就大.D选项,因为REPORT TO AUTHORITY的都是严重例子,故百分比大,而不是实际死亡的比例大.故WEAKEN

liy_lilan

原来如此，多谢啦！