be able to可接被动形式吗?复习书上写be able to一般不接被动形式,但是如果把“They are able to overcome the difficulties.”改写成“The difficulties are able to be overcome by themselves”算错吗?是by them 打错了

be able to可接被动形式吗?复习书上写be able to一般不接被动形式,但是如果把“They are able to overcome the difficulties.”改写成“The difficulties are able to be overcome by themselves”算错吗?是by them 打错了 be able to能接动词不定式的被动形式吗? be able to能否有被动语态? be able to能否有被动语态? be able to 否定形式是什么? 关于able的用法辅导书上说able接不定式时,只能接肯定的、主动的不定式,不能接被动的不定式.需要时可由can代替：His voice was not able to be heard.（误)His voice couldn't be heard.（正）但朗文字典上给 be able to的现在完成时形式为_________able to? I imagine sb.to be able to do sth.为什么这里是 to be able 的形式? be able to 用法 be able to中文 able to be assigned be able to be able to (送分拉) 请问：be able to be able to 意思 turn out to be有没有被动形式? not be able to =be unable to? 这个词组的否定形式是什么 They might be able to afford a new car .be able to 能用can替代吗?