The new buyer identified a dozen new sources for the material, proved to be reliable．
A. most of them
B. most of which
C. most of whom
D. most of those
网友回答
A. most of them
(答案→)B. most of which
C. most of whom
D. most of those
解析：句意：新的买方确定了十几个新的来源为材料，大部分被证明是可靠。先行词是物the material，应该用which做介词宾语，引导非限制性定语从句，whom代人，其他表示定语从句的关系词，故选B。
考点: 考查定语从句的用法。