There is an ample evidence, derived from the lore of traditional folk medecine, that naturally occuring antibiotics are usually able to be modified to make them a more effective drug. (B) are usually able to be modified to make them more effective drugs (C) are usually able to be modified, which makes them more effective drugs (D) can usually be modified to make them a more effective drug (E) can usually be modified to make them more effective drugs. 答案是E 请问be able to和can有什么区别?具体到这个句子中呢? 谢谢:) |