can, could 和be able to的用法

She can/be able to sing the song in English. This machine can make you feel comfortable.

1.can, be able to都可表示“能力”

Can的主语是人或物,be able to的主语是人

We’ll be able to finish the work soon. I haven’t been able to see the film.

2.can只用于现在式和过去式(could)。be able to可以用于各种时态。

could用于表示泛指过去的能力。如： I could read when I was four.