---Did they have a good time at the party?---Judging by their smiles, they _________ have enjoyed themselves.

—What does the sign over there read?—No person ________smoke or carry a lighted cigarette ,cigar or pipe in this area. 

 Don’t be angry with us. We _____ with you together, but we were busy with our final reports when you called in.

________ people used the computer thirty years ago, but now it’s very popular.

—Excuse me. Is this the right way to the Summer Palace? —Sorry, I am not sure, but it ____ be.