He worked late into the night yesterday. That’s he couldn't get up on time this morningA.

问题补充：

He worked late into the night yesterday. That’s he couldn get up on time this morning

A. how

B. why

C. what

D. when

答案：

A. how

(答案→)B. why

C. what

D. when

解析：这是以why引导的表语从句.意为:那就是今天早上他为什么不能按时起床的原因.