On stepping into the room this morning, I was astonished to find the floor covered with looked like tiny insects.
A. that
B. what
C. where
D. when
网友回答
A. that
(答案→)B. what
C. where
D. when
解析：通过分析句子结构，可知这个句子中包含一个宾语从句，这个宾语从句是作介词的宾语。且引导词在从句中主语，表示“什么”的意思，故用what 。