Lately some scientists are experimenting ___________ white mice to ____________ this kind of medicine.
| A．on,try on | B．with, test on | C．on ,test out | D．with,carry out |
31. — I'm wondering why the visitors chose to stay with the host family.
— _____real local life.
| A．Experiencing | B．Experience | C．To experience | D．Having experienced |
30. How long do you think it will be _____ we can find a new water source?
| A．after | B．before | C．when | D．Since |
29. High up in the mountains _____ a quiet small village, with only 20 households.
| A．surrounds | B．locates | C．lies | D．Lays |
28. A heavy snow promises a good harvest, _____ is often the case.
| A．where | B．as | C．that | D．What |
27. After his wife died, he kept himself _____ from other people and the outside world,
| A．set off | B．cut off | C．put off | D．taken off |