His mother _____ teacher.
You can never imagine what great trouble I have had ______the patient who receive a serious wound.
______ of the land in Jia Xing No. 1 Middle School _______ covered with trees and grass.
As is known to all language learners, the newly learnt words will soon be forgotten unless______ used in everyday communication.
The last thirty years _________ the quick development in almost every field in China.
The dog, if trained _____, will be made a good watch-dog one day.