XDF section15 Q13

Biologists working in Spain say that their discovery of teeming life in a highly acidic river may not only broaden the search for life, or for evidence of past life, on other planets but also show that a number of forms of microscopic life can adapt to conditions that scientists have long thought hostile to all but the hardiest bacteria.

A. show that a number of forms of microscopic life can adapt to conditions that scientists have long thought hostile to all but the hardiest bacteria
B. may show that a number of forms of microscopic life is capable of adapting to conditions that scientists have long thought hostile to all bacteria but the hardiest ones
C. shows a number of forms of microscopic life to be capable to adapt to conditions that scientists have long thought had been hostile to all but the hardiest bacteria
D. showing that a number of forms of microscopic life is capable of adapting to conditions that scientists have long thought had been hostile to all but the hardiest bacteria
E. showing that a number of forms of microscopic life can adapt to conditions that scientists have long thought hostile to all bacteria but the hardiest

答案是A,为什么不是C呢?用SHOWS不是更好吗?主语是单数的discovery

根据not only, but also的平行直接得到答案

....discovery may not only do ...but also do