He couldn't be there at that time because I waited for him all day.

问题描述:

He couldn't be there at that time because I waited for him all day.

他那个时候肯定不在那里,因为我等了他一天(都没看到他)

couldn be 在这里表推测

你好,很高兴能够在这里回答你的问题,这道题的正确答案应该为:
那个时候他不可能在那儿,因为我一整天都在等他.