—Did you find the missing couple in the mountain yesterday?
—No, but we ________ to get in touch with them ever since.
| A．have tried | B．have been trying | C．had tried | D．had been trying |
One way to understand thousands of new words is to gain _____ good knowledge of basic word information.
| A．不填 | B．a | C．the | D．one |
It was announced that only when the fire was under control ____ to return to their homes.
| A．the residents would be permitted |
| B．had the residents been permitted |
| C．the residents had been permitted |
| D．would the residents be permitted |
The driver _____ for the accident had not been driving carefully.
| A．blamed | B．being blamed |
| C．to be blamed | D．blaming |
You should read the _________ in the car repair manual (手册) carefully before you start to work on it.
| A．instructions | B．descriptions |
| C．introductions | D．explanations |
_____ to nuclear radiation, even for a short time, may produce variants (变异体) of genes in human bodies.
| A．Exposed | B．Being exposed |
| C．Having exposed | D．After being exposed |