You can only be sure of _____ you have at present;you cannot be sure of something _____ you might get in the future.
If Harry did not attend the conference last night, he________too much work to do.
There was a lot of fun at yesterday's party. You________come, but why didn't you?
—John, how did your maths exam go?—I thought I________, but in fact I came in the top ten in the class.
As you worked late yesterday, you________have come this morning.
The weather turned out to be fine yesterday. I________the trouble to carry my umbrella with me.