一、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。 二、be able to 后面接动词原形，表示能够做某事 He is able to drive a car.他会开车。 They are able to sing the song.他们能够唱这首歌。 三、be able to 的时态 一般现在时：am/is/are able to I am able to run very fast.我能够跑得非常快。 一般过去时：was/were able to He was able to make lots of friends when he was young.当他年轻的时候，他能够交很多朋友。 一般将来时：will be able to They will be able to finish the work soon.他们很快就能够完成工作。 现在完成时：have/has been able to I wonder whether they have been able to find jobs.我想知道他们是否（已）能够找到工作。 Many women have been able to pick up the threads of their former career. 许多女性得以重操旧业。 四、be able to 的否定式 一般现在时：am not/isn’t/aren’t able to I'm not able to understand this math problem.我不能理解这道数学题。 一般过去时：wasn’t/weren’t able to My legs failed me and I wasn't able to run the last lap. 我这腿不争气，最后一圈跑不动了。 一般将来时：won’t be able to Jack won't be able to come for another three days.杰克再过三天就不能来了。 现在完成时：haven’t /hasn’t been able to We haven't been able to get in touch with them yet. 我们还没能与他们取得联系。 五、be able to 的同义词 was/were able to ≈ could am/is/are able to ≈ can wasn’t/ weren’t able to ≈ couldn’t （最常用） am not/ isn’t /aren’t able to ≈can’t be able to 的否定式与 be unable to 同义 比如： Many families on low incomes will be unable to afford to buy their own home. = Many families on low incomes will not be able to afford to buy their own home.许多低收入家庭将会买不起自己的房子。
