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
23._______, the driver looked at the vast desert without knowing if he could get across safely.
A. Tiredly and sadly B. Tired and sad
C. Tired and sadly D. Tiredly and sad
24. It was foolish of you to take a taxi ______you could easily walk there in fiv
