我纠结在相同的选项上!1：Within a few years he had written five books,no

我纠结在相同的选项上!
1：Within a few years he had written five books,none___could be easily classified as novel.
A.of whom
B.of them
C.of which
D.in which
2：The factory produces half a milllion pairs of shoes every year,80％____are sold abroad.
A.of which
B.which of
C.of them
D.of that
我想问一下,这两道题为什么不能都选of them