Small sailboats can easily turn over in the water ______ they are not managed carefully.
| A．though | B．before | C．until | D．if |
20．—Though it is 30 years _____ we last met, I still remember the scene _____ we got separated on a rainy day.
| A．since; where | B．before; which | C．since; when | D．before; where |
19．—My cat’s really fat.
—You ______ have given her so much food.
| A．wouldn’t | B．couldn’t | C．mustn’t | D．shouldn’t |
18．—Jim, are you ______ this Saturday?
—Oh, sorry. I need to go to the bookshop _____ the bank on Saturday.
| A．convenient; and | B．convenient; as well as |
| C．available; as well as | D．available; with |
17．I _______there little more than a week when I set to work with the scientist.
| A．would be | B．had been | C．have been | D．will be |
16．—Tom, you’ve got an A in the final English exam. Congratulations!
—Thanks. But I never thought the result came out so fast. The papers _____ when I left the teacher’s office just now.
| A．had been marked | B．were still being marked |
| C．are still marking | D．had been marking |