___ years ago, the population of China was over 20 million.
I was just falling asleep ____ there was a loud knock at the door.
----Can you tell me if he ________ ? ----If he _________, I will call you.
There are many shops on ________ side of the street.
The policeman warned the driver _______too fast. It was very dangerous.
It is important for usEnglish well.