GWD22-Q5 求助，请NN们帮忙分析！

snail007

The dry mountainranges of the western United  States
contain rocks dating back 440 to 510million years, to the Ordovician period, and teeming with evidence of tropicalmarine life. This rock record provides clues about  one of the most significant radiations  (periods when existing life-forms gave rise tovariations that would eventually evolve into entirely new species) in thehistory of marine invertebrates. During this radiation the number of marinebiological families increased greatly, and these families included species  that would dominate the marine ecosystems ofthe area for the next 215 million years. Although the radiation spanned tens ofmillions of years, major changes in many species occurred  during a geologically short time span withinthe radiation and, furthermore, appear to have occurred worldwide, suggestingthat external events were major factors in the radiation. And , in fact, thereis evidence of major ecological and geological changes during this period: thesea level dropped drastically and mountain ranges were formed, in thisinstance, rather than leading to large-scale extinctions, these kinds ofenvironmental changes may have resulted in an enriched pattem of habitats andnutrients, which in turn gave rise to the Ordovician radiation. However, theactual relationship between these environmental factors and the diversificationof life forms is not yet fully understood





    
Q5. Which of thefollowing can be inferred from the passage regarding the geologic changes thatoccurred during Ordovician period?

A.   They were more drastic than those associatedwith other radiations

B.   They may have created conditions favorableto the evolution of many new life-forms

C.   They may have caused the extinction of manyof the marine species living in shallow waters

D.   They may have been a factor in thedevelopment of new species adapted to living both on land and in water

E.    They hastened the formation of the extensivedry regions found in the western united states


答案是E。 为什么B不对啊？

gaoryan

http://forum.chasedream.com/GMAT_RC/thread-339763-2-1.html