16. —Who____ it be that is knocking at the door? —It ____ be Father, but I’m not sure.
If you go on doing so, you’ll _______ yourself sooner or later.
—Why are you so busy, Mike ? —I ______ a novel these days.
If you want to book tickets for a film in Qionghai, just call 62838009. It _______be simpler.
Rather than ________on a crowded bus, he always prefers _______a bicycle .
You can take any seat _______ is free.