21．-- Would you like to visit Shantou City with me this summer vacation?
-- No． I ________ it before． Besides, it's hot and humid in summer．
A．visit B．visited C．will visit D．have visited
22． —What’s wrong with your left hand?
—I got it ______ in the door．
A．catching B．caught C．to be caught D．to catch
23．We asked John and Henry some easy questions, but of them could answer them．
A．none B．neither C．all D．both
24．She wants to know ______ speak English．
A．if I can B．if can I C．whether I D．whether could I