请问大全section3-6

There is ample evidence, derived from the lore of traditional folk medicine, that naturally occurring antibiotics are usually able to be modified to make them a more effective drug.

(A) 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）

(E) can usually be modified to make them more effective drugs

没有找到这一题的链接解释，想问问为什么b不正确？谢谢

be able to不能加被动？！

原来是这样呀，还好发帖问问，要不都不知道这个语法点！

谢谢dreadpower!!!!!

我想补充一点

be able to 表示有能力 通常用于人或其它有”能力”的东西

当主辞为非生物时,如果如果用be able to 就要小心,GMAT通常用can

如果想再深入,建议去查查英英字典 你会了解

Can , be able to 的差别

怪不得我就觉得好像can都是优先于be able to选择的，谢谢vaporization的补充！！