.—Steve come back because the window is open. —Yes.but he _______left it open last night.
Once ___ what to do, these computers will show great power in carrying it out.
He talked about the classmates and the school ___ he had visited.
Americans eat __ vegetables per person today as they did in 1910.
I wonder if you know it ___ .
The number of people invited ___ fifty, but a few of them ___ absent for different reasons.