问题补充:
Which materials can be thrown into the sea on the nature of them?
A. depended
B. depending
C. to depend
D. depends
答案:
A. depended
B. depending
C. to depend
(答案→)D. depends
解析:考查主谓一致。本题中的Which materials can be thrown into the sea是一个主语从句,当一个单独的主语从句做主语的时候,谓语动词使用单数的形式。故D正确。