If the balance of nature is ____ , a series of problems will arise .
| A．disturbed | B．troubled | C．interrupted | D．confused |
It was 80 years before Christopher Columbus crossed the Atlantic______ Zheng sailed to East Africa
| A．when | B．that | C．after | D．since |
All of my teachers but the math teacher ______ he cheated in the exam.
| A．doubt that | B．doubts that | C．doubt whether | D．doubts whether |
The teacher told us that everyone has an important role ________in protecting the earth from________.
| A．to play; to pollute | B．to be played; to be polluted |
| C．to play; being polluted | D．to be played; being polluted |
When I enter this classroom, I always feel the ______ pressure of study, for I have so many opponents to compete with.
| A．invisible | B．invaluable | C．insensible | D．impolite |
Those who failed to get into the art exhibition ________ disappointed as many of the artists who should have appeared did not come.
| A．didn’t need feel | B．needn’t have felt |
| C．mustn’t have felt | D．couldn’t have felt |