It is hard to say what kind of person he is. Sometimes he is very friendly; at other times he ___ be very cold.
We were about to start out________ our friends called us up from Shanghai.
He suggested the person referred________ put into prison.
My mother liked this kind of dress________ and bought some material to make one at home.
You have no idea how she finished the relay race________ her foot wounded so much.
It’s high time that we students________ harder as the examination is drawing nearer.