The factory used 65 percent of the raw materials,the rest of whichsaved for other purposes

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A. is
B. are
C. was
(答案→)D. were
解析：D解析：考查主谓一致和时态。由主句可知应用一般过去时。the rest of which中which指代的是复数名词
materials，故谓语动词用复数形式。
【规律总结1“the+形容词”表示一类人时，作主语，谓语动词用复数。但the rest，the remainder作主语时，若指代可 ，数名词，谓语动词用复数；若指代不可数名词，谓语动词用单数。