70. A low-pressure weather system is approaching Plainville; rainfall results from about 70 percent of such systems in the LACE w:st="on">PlainvilleLACE> 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 LACE w:st="on">PlainvilleLACE>.

Knowing which one of the following, in addition to the information above, would be most useful for determine the probability that LACE w:st="on">PlainvilleLACE> will have a thundershower soon?

A. the percentage of thundershowers in LACE w:st="on">PlainvilleLACE> that occur in the spring

B. the percentage of spring rainfalls in LACE w:st="on">PlainvilleLACE> 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

参考答案：C

思路：文中给出两个条件，1是低压天气将到达，而70%的低压天气导致降雨，2是现在正是1年中雷阵雨最多的季节且雷阵雨有时也是由于低压天气导致；答案（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了。

A、B没能和低压天气联系起来，D、E为无关选项

“用70%乘以这个比率，就可以得到下雷阵雨的概率了”是不是有那么一DD问题呢？用任何的比率×70％肯定少于70％，但是很明显题目中的两个条件是并列的，两个条件是比只有一个条件进一步增加了thundershower的可能性，那又怎么可能是比率相乘呢？？？

thundershower的概率估计应该是1－[（1－70％）×（1－？％）]才对～～～～