单选题
[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__________.
A.Killing Power of Ancient Volcanic Eruptions
B.Accounting for the Killing Power of Older Eruptions
C.Calculation of the Killing Power of Older Eruptions
D.A Mass Extinction
正确答案：C
答案解析：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。