—It’s time that I ____ on night duty. I must be off now.—I’d rather you ____ at home on such a family reunion night.
The children ________ lost in the woods; otherwise, they would have been at the lakeside camp as scheduled.
—Why are your eyes so red? You ________ have slept well last night. —Yeah, I stayed up late writing a report.
Some young people these days just ________ go out of their homes to contact the real world.
Why ________ it get colder when we climb up a mountain? We are getting nearer to the sun!
I ________ to my cousin's birthday party last night, but I was not available.