Parents should encourage their children to __________ in all kinds of activities to train their ability of teamwork.
| A．participate |
| B．donate |
| C．devote |
| D．witness |
You can’t imagine what great trouble they have _____ the problem _____.
| A．to solve; being talked about |
| B．solving; discussing |
| C．to solve; to talk about |
| D．solving; being discussed |
In January , 2004, the United States successfully launched “Spirit”, a Mars Exploration Rover, _____ a new milestone in the history of mankind.
| A．it marked | B．marking | C．marked | D．to mark |
He looked around and caught a man _____ his hand into the pocket of a passenger.
| A．put | B．to be putting | C．to put | D．putting |
--- I’m sorry, but there’s no smoking on this flight.
--- Oh, I ______ that. Sorry, I won’t again.
| A．don’t know | B．didn’t know |
| C．won’t know | D．haven’t known |
--- I dropped in at your house at about ten last night, but you weren’t in.
--- I ______ regular exercises at the club.
| A．did | B．was doing | C．had done | D．have been doing |