Barack Obama delivered a speech to 500 local youths during his visit to China, many of were from Fudan University and Tongji University.
A. them
B. whom
C. which
D. those
网友回答
A. them
(答案→)B. whom
C. which
D. those
解析：考查非限制性定语从句。先行词是500 local youth，指人用who/whom/that，排除C；根据逗号判断，是非限制性定语从句，有and的话，是并列分句，A、D不能引导定语从句，排除A、D；故选B。