----Do you know how toa crying baby?---Sorry I don’t know . I think it’s too hard.A. fall

问题补充：

----Do you know how toa crying baby?

---Sorry, I don’t know . I think it’s too hard.

A. fall down

B. turn down

C. put up

D. calm down

答案：

A. fall down

B. turn down

C. put up

(答案→)D. calm down

解析：fall down失败，倒塌；turn down关小，调低；put up提供，建造；calm down镇定下来。句意：你知道如何让一个哭泣的婴儿平静下来吗？——抱歉，我不知道。我认为太难了。结合语境可知选D。