On weekends,the supermarket is very ________.
By the time of last year, she ______ the piano for five years.
—Listen! Peter is singing in the classroom!—It _____ be him. He has gone back to his hometown.
Keys _______ opening the lock in the door.
—I have never been to the Great wall. —If you have an opportunity _______ there, you must take it.
There was _____ woman in the room, sitting and looking at me in the dark.