Country life gives him peace and quiet, which is ________ he can't enjoy while living in big cities.
Mr. Li is absent today. What do you consider ________ to him?
The reason ________ he refused to attend the meeting was that they didn’t give him an invitation earlier.
Our English teacher requested that the homework ________ tomorrow morning.
Smoking, which may be ________ fun for some people, is ________ cause of discomfort for the people around him.
— I was worried about math, but Mr. Brown gave me an A!— ________ That’s a difficult course.