单选题 Some of the experiments ______ in our textbook were very difficult to carry out.
A. to describe B. described
C. describing D. to have described

【正确答案】 B
【答案解析】[考点] 非谓语动词。当作后置定语的分词与被修饰的名词表示被动关系时，要用动词的过去分词。故选B。