There are still many problems ______ before we are ready for a long stay on the Moon.
| A．solving |
| B．solved |
| C．being solved |
| D．to be solved |
Nuclear science should be developed to benefit the people _____ harm them.
| A．better than | B．more than | C．other than | D．rather than |
It is a great pleasure for a woman to ________ the price while shopping.
| A．cut in | B．cut down | C．cut off | D．cut up |
. ______ the ancient Egyptians built the pyramids puzzled people for centuries.
| A．Whether | B．What | C．How | D．Where |
No one but the experts in this field can _____ the difference between them.
| A．recognize | B．speak | C．spot | D．predict |
—Who______ it be that is knocking at the door?
—It ______ be Father, but I’m not sure.
| A．can; must | B．can; may | C．must; can | D．may; must |