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