【题目】He wrote many children' s books, nearly half of _______were published in the 1990s.
A.whom
B.which
C.them
D.that

【答案】B
【解析】句意：他写了许多儿童书籍，几乎一半在1990年左右出版。先行词是books，定语从句中of缺少宾语，故选B项。