从A、B、C、D四个选项中, 选出可以填入空白处的最佳选项。
21. As _________ mountains beyond our village are becoming greener and greener, they have become_________ home to a large amount of wild life.
A. the; / B. the; a C. /; / D. the; the
22. The third summit of the Group of 20 (G20) ________ in Pittsburgh, Pennsylvania on the evening of September 24, 2009.
A. took off B. kicked off C. put off D. set off
