The company used 50 percent of the raw materials, the rest of which sent to other cities

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A. is
B. was
C. are
(答案→)D. were
解析：考查主谓一致。本题定语从句的先行词是the raw materials，which知道先行词作为of的宾语，当the rest做主语的时候，谓语动词的单复数要看后面的名词，如果后面的名词是复数形式的名词，谓语动词使用复数形式。根据used说明本句是一般过去时。故本题选择D项。