could do sth in their sleep字面意思：睡觉的时候也能做… 梦里也能做…（梦里都能做成某事，也就表示非常容易的做此事，通常是因为他常常做此事。）

【例句】
I’ve done this recipe so many times, I could do it in my sleep now.
我做这个食谱很多次了，现在我在梦里也能做它。

I have done this type of question many times,I could do it in my sleep now.
这种题型我做过很多次了，现在我在梦里也能做。