_____ 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 |
33. Is it the letter you got yesterday ________ makes you so sad?
| A．what | B．that | C．how | D．When |
32. It’s important to listen to your teacher carefully in class, so try not to let your mind _________.
| A．lose | B．stop | C．wander | D．Disturb |
31. －Do you mind if I turn off the TV?
－__________.
| A．Yes, please | B．No, go ahead | C．Yes, you can | D．No, I’d rather you didn’t |
30. Jennifer, who is my best friend, said she would go abroad for further education __________.
| A．before long | B．long before | C．shortly after | D．very fast |
29. A good teacher should leave some time for the students to _________ the knowledge.
| A．introduce | B．receive | C．digest | D．Accept |