Mary was born in 1998 and she began to play _______ guitar at the age of seven.
A.a B.不填 C.the
—Could we go and watch the football game?
—No, ______ you have the tickets.
| A．if | B．unless | C．because | D．since |
—Can I go to the park, Mum?
—Certainly. But you ______ be back by six o’clock.
| A．can | B．may | C．might | D．must |
—I’m leaving now.
—______ you turn off the lights and the computer.
| A．To make sure | B．Make sure | C．Made sure | D．Making sure |
The population problem may be ______ one of the world today.
| A．the most | B．most difficult | C．the greatest | D．more interesting |
Don’t ______ so often. It’s bad for your health.
| A．get up | B．stay up | C．look up | D．come up |