Điền từ thích hợp vào chỗ trống, hoàn thành câu

18. The teacher asked me if I knew ______ the machine.
A. how to operate   B. to operate   C. operating   D. how operate
19. He'd prefer ______ chicken soup rather than _____ milk.
A. having/ drinking   B. to have/ drink   C. have/ drink   D. had/ drank
20. May I _____ your telephone?
A. use   B. useful   C. useless   D. using
21. For the most part, young children spend their time _____
A. played   B. to play   C. played  D. playing