为什么be able to do 有各种时态变化,而can(could)仅有过去时呢?这是上课做的笔记,我有点不理解．

为什么be able to do 有各种时态变化,而can(could)仅有过去时呢?这是上课做的笔记,我有点不理解． be able to do和do有什么区别. be able to do sth I imagine sb.to be able to do sth.为什么这里是 to be able 的形式? be unable to do与be not able to do有什么区别 able to do be able+不定式有这样的短语吗? 用be able to do sth造句 be able to do sth 等于什么 be able to do sth 意思 用法! 英语 翻译 be able to do sth 怎样用be able to do造句? be able to do sb.a faver Do not you be able to Will she ( ) do the work?A.be able to B.able to C.is able to be able to do sth be able to do sth 的同义词是什么? 关于be able to do will you be able to come to a meeting next week?will是be 动词.为什么要多+个be 难到不是 will you able to come to a meeting next week? may not able to do sth 还是 may not be able to do sth? if he study hard,he will ( ）learn English well.里面应该填什么?选项有：be able to,is able to,can,able to,为什么?