they heard the noise of traffic (the next morning)对括号部分提问
问题描述：
they heard the noise of traffic (the next morning)对括号部分提问
snowballs hit beijing (three) times last year.
the boy studies very hard (because he wants to be a top student in his class)
答
When did they hear the noise of traffic?
How many times did snowballs hit beijing last year?
Why does the boy study very hard?