关于 be able 我看语法书上写的be able to表示成功的做成某事,不能用could.而新概念2册的62课 F
关于 be able
我看语法书上写的be able to表示成功的做成某事,不能用could.而新概念2册的62课 Firemen had been fighting the forest fire for nearly three weeks before they could get it under control.这里为什么不用be able to?不是成功的做成某事不能用could的吗?把我搞糊涂了