Ladies and gentlemen, please fasten your seat belts. The plane __________.
| A．takes off | B．is taking off |
| C．has taken off | D．took off |
I _____ it as a basic principle of the company that suppliers of raw materials should be given a fair price for their products.
| A．make | B．look | C．take | D．think |
Small sailboats can easily turn over in the water ______ they are not managed carefully.
| A．though | B．before | C．until | D．if |
. Leaves are found on all kinds of trees, but they differ greatly ________ size and shape.
| A．on | B．from | C．by | D．in |
Reality is not the way you wish things to be, nor the way they appear to be, ___ the way they actually are.
| A．as | B．or | C．but | D．and |
People try to avoid public transportation delays by using their own cars, and this _____ further problems.
| A．in short | B．in case | C．in doubt | D．in turn |