费费135-70

70. A low-pressure weather system is approaching Plainville; rainfall results from about 70 percent of such systems in the Plainville area. Moreover, the current season, spring, is the time of year in which thundershowers, which sometimes result from low-pressure systems, are most likely to occur in Plainville.

Knowing which one of the following, in addition to the information above, would be most useful for determine the probability that Plainville will have a thundershower soon?

(A) the percentage of thundershowers in Plainville that occur in the spring

(B) the percentage of spring rainfalls in Plainville that are thundershowers

(C) the percentage of thundershowers in Plainville that result from low-pressure systems

(D) whether low-pressure systems in other areas are associated with rainfall

(E) whether Plainville has more or fewer thundershowers each spring than do near by towns

答案是C,详解版给出的解释是:（C）给出了低压天气导致雷阵雨的比率，用70%乘以这个比率，就可以得到下雷阵雨的概率,A、B没能和低压天气联系起来，D、E为无关选项

但按照以上解释我觉得应该是b对,原文给出的关系是LP有70%的概率会下雨,如果再给出下的雨中是thundershowers的概率(假设是x)就可算出LP会导致thundershowers的概率,即70%乘以x.而b中给出的是如果是thundershowers则是由LP导致的概率,这与给出的解释的方向不一致.

望高手赐教!