Recently our community has launched a campaign among all the residents , we are called up

Recently our community has launched a campaign among all the residents , we are called upon to do our little but to prevent the worsening environment.
A. where
B. which
C. as
D. when

(答案→)A. whereB. whichC. asD. when解析：句意：最近我们的社区已经在所有的居民中发起了一项运动,我们被要求我尽我们的力量来防止环境恶化。这里使用了定语从句，先行词是a campaign，后面是非限制性定语从句，从句中不缺少主宾表，缺少的是地点状语，所以用where引导定语从句。选A。

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