问题
选择题
21．In recent years global warming has become concern for people all over the world.
A．the, the
B．/,/
C．/, a
D．the, /
答案
答案：C
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21．In recent years global warming has become concern for people all over the world.
A．the, the
B．/,/
C．/, a
D．the, /
答案：C
