be able to=be capable of。当be able to解释为能够做某事的时候，can=be able to；当be able to表示“（过去）成功做”时，be able to=manage(d) to do=succeed(ed) in doing=be successful in doing.
be able to翻译
表示“能够做某事”，强调通过努力而获得的能力。
She is able to play the piano.
她能够弹钢琴。
I am able to drive the truck.
我能够开那辆卡车。
She is able to speak three languages.
她能够讲三种语言。