couldyou的用法归纳高中

作为 can 的过去式，表示能力， 能做某事。
Lily could play the piano by the time she was only six.
莉莉六岁时就能弹钢琴了。
They couldnt afford to buy a new car, so they chose a secondhand one.
他们买不起新车，只能选一辆二手的。