Once having made a promise,you should keep it.为什么have要用进行时having?还有为什么shall要用过去时should?

分类: 作业答案 • 2021-12-19 16:19:46

问题描述：

Once having made a promise,you should keep it.
为什么have要用进行时having?还有为什么shall要用过去时should?

答