You will find the game is not so difficult to play ______ you understand its rules.
| A．until | B．since | C．before | D．once |
Stop making noise, _______ the neighbors will start complaining.
| A．so | B．but |
| C．and | D．otherwise |
Many students go to school _______ the tube in Beijing every day.
| A．with | B．for |
| C．on | D．at |
It was two weeks before the Spring Festival and the shopping centre was _____ with shoppers.
| A．full | B．crowded |
| C．satisfied | D．noisy |
Leave your key with a neighbor _____you lock yourself out one day.
| A．ever since | B．even if |
| C．soon after | D．in case |
—Bob has gone to California.
—Oh, can you tell me when he ______?
| A．has left | B．left |
| C．is leaving | D．would leave |