Americans eat _______ vegetables each person today as they did 20 years ago..
The person we spoke to ____ no answer at first.
You can never imagine what great difficulty I have _____ your house.
Before he went abroad, he spent as much time as he ____ English.
Mr. Wang made up his mind to devote all he could ____ his oral English before going abroad.
It was quite a serious accident, _________ caused by careless driving.