题目类型：
单选题
题目内容
【概括大意】Wignall calculated the "killing efficiency" for these volcanoes by comparing the proportion of life they killed off with the volume of lava that they produced. He found that size for size, older eruptions were at least 10 times as effective at wiping out life as their more recent rivals.The main idea of this paragraph is__________.
正确答案
C
题目解析
本段第一句话是说：Wignall calculated the "killing efficiency" for these volcanoes…；Wignall 计算了这些火山的“灭绝效率”……；其中killing efficiency与killing Power意思差不多，属于同义词转换，因此选择B或C，但是account for 意思是：(在数量方面)占；说明(原因等)不符合句意，因此不选择B。
AI解析
本段主要讲述了Wignall通过比较火山造成的生命损失比例和火山喷发产生的熔岩体积来计算这些火山的“灭绝效率”。他发现，对于相同规模的火山来说，较古老的喷发在灭绝生命方面至少比最近的喷发有效10倍。因此，本段的主旨是关于计算古老火山喷发的“灭绝效率”。选项C“计算古老火山喷发的灭绝效率”最符合这段文字的主旨。