If you are in any doubt as to _____ you should be doing these exercises, consult your doctor.

The policeman came up to the house, whose door was open, _____ there for a while, and went in

The old man can’t hear us well because there’s something wrong with his ______.

Tony likes reading books.—But Bettyenjoys________for things on the Intemet．

The girl’s _____ voice and excellent performance made her stand out in the singing contest.