When he came back from abroad, Joan told us about the cities and the people he had visited.
A. that
B. who
C. where
D. which
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(答案→)A. that
B. who
C. where
D. which
解析：考查定语从句。本定语从句的先行词是the cities and the people,既有人又有物，所以使用that指代先行词在定语从句中做visit的宾语。B只能指人，D只能指物。C在句子中做状语。