---- What happened to you?
---- I ________ in the street when someone patted me on the shoulder, which frightened me.
| A．was about to walk | B．was walking |
| C．had walked | D．walk |
_______ in the queue for half an hour, Tom suddenly realized that he had left his wallet at home.
| A．To wait | B．Having waited | C．Have waited | D．To have waited |
_______ to sunlight for too much time will do harm to one’s skin.
| A．Being exposed | B．Exposed |
| C．Having exposed | D．After being exposed |
The bell _______ the end of the period rang, _______ our heated discussion.
| A．indicated; interrupting | B．indicating; interrupting |
| C．indicating; interrupted | D．indicated; interrupted |
The research is so designed that, once _______, nothing can be done to change it.
| A．begins | B．having begun | C．begun | D．Beginning |
The most important thing _______ we should pay attention to is the first thing ________ I have said.
| A．which; that | B．that; which | C．that; that | D．which; which |