21．In recent years global warming has become concern for people all over the world.A. the,

发布时间：2020-08-29 23:35:41


21．In recent years      global warming has bee     concern for people all over the world.
A. the, the
B. /,/
C. /, a
D. the, /

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A. the, the
B. /,/
(答案→)C. /, a
D. the, /
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