He is able to axplain the ______(原因) because he was there at that time.

问题描述:

He is able to axplain the ______(原因) because he was there at that time.

He is able to axplain the _reason_(原因) because he was there at that time.为什么不加s没有明确说明单复数,加不加s都可以为什么我加了s算错不清楚,按照我的理解加不加都没有问题。。。