.In order to prevent the fire spreading, some of the houses nearby _____before the firemen arrived.
| A．have been pulled down | B．have pulled down |
| C．had been pulled down | D．had pulled down |
32．Tens of thousands of trees _____ in the area in the past few years．
| A．have been planted | B．were planted | C．have planted | D．had planted |
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 |