feifei_logic70求教

【feifei_logic】70. A low-pressure weather system isapproaching Plainville; rainfall results fromabout 70 percent of such systems in the Plainvillearea. Moreover, the current season, spring, is the time of year in whichthundershowers, which sometimes result from low-pressure systems, are most likelyto occur in Plainville.

Knowing whichone of the following, in addition to the information above, would be mostuseful for determine the probability that Plainvillewill have a thundershower soon?

A.     the percentage ofthundershowers in Plainvillethat occur in the spring

B.     the percentage of springrainfalls in Plainvillethat are thundershowers

C.     the percentage ofthundershowers in Plainvillethat result from low-pressure systems

D.     whether low-pressure systems inother areas are associated with rainfall

E.     whether Plainville has more or fewer thundershowerseach spring than do near by towns

答案：C

题目给了两条信息：①低气压70%的概率导致降水；②雷阵雨也可能由低气压导致

C选项给了由低气压导致雷阵雨的概率，为什么相乘就是该地区雷阵雨的概率？

我个人认为应该是B啊，低气压导致降水概率×降水中打雷概率不就等于该地区雷阵雨概率？

求解答