(一).I don't know what's keeping him. 我不知道他为什么迟到。
原音重现：

A：Why is Sam late for this meeting?
萨姆为什么开会迟到？
B: I'm not sure. I don't know what's keeping him.
是呀，不知道为什么迟到了。

(二).What took you so long? 做什么用了这么久？

原音重现：

A：What took you so long?
为什么迟到了？
B: I had to go change my clothes.
我换衣服来着。