21.Sorry, I'm late. I ____have turned off the alarm clock and gone back to sleep again.
A．might B．should C．can D．Will
22. My sister has some trouble ______spelling some of the words in American English, while I have some difficulty ________ my pronunciation．
A．with; with B．in; with C．with; in D．in; in
23. Someone is ringing the doorbell．Go and see ________
A．who is he B．who he is C．who is it D．who it is
