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As a result we work hard ______ the task of saving time.
A、in
B、to
C、at
D、for
【正确答案】：C
【题目解析】：本题考查work hard的用法。work hard to do sth.努力做某事；work hard at sth.努力完成某事。work hard for sb.为某人努力工作；一般不与in连用。work hard to接do sth.,故排除B；D项不符合题意。答案为C。