____ of the land in that district ____ covered with trees and grass.
| A．One half; are | B．Two seventh; is |
| C．A quarter; is | D．Two thirds; are |
26．______ I'm willing to help, I do not have much time available．
| A．While | B．When | C．Once | D．Since |
25．The rise of oil prices made scientists search for new energy resources ______ oil．
| A．replace | B．replacing | C．to replace | D．Replaced |
24．You didn't believe John won the first prize at the speech competition, ______?
| A．did he | B．didn't he | C．did you | D．didn't you |
23．I had reached a point in my career _____ I needed to decide which way to go．
| A．why | B．which | C．when | D．Where |
22．Here are some new computer programs _____ for home buildings．
| A．designing | B．design | C．to design | D．Designed |