Those were the graduate assistants ______ to do the research work in the lab.
A.to whom it was their responsibility
B.whose responsibility there was
C.whose responsibility was
D.of whom with the responsibility
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C解析此题考查属格关系代词引导的定语从句，[A]、
D.项应先排除；
B.项从句的谓语为there be结构，讲不通；因此只有[C]项为正确