----- How did you know the surprising news?----- I happened _______ the event then.
The flu is believed ________ by viruses that like to reproduce in the cell inside the human nose and throat.
________ the meeting himself gave them a great deal of encouragement.
—They are quiet,aren't they? —Yes.They are accustomed ________ at meals.
The news of ________ greatly made us surprised a lot as he was indeed very excellent.
________ the program,they have to stay there for another two weeks.