单选题 When she was awake, she found that she was standing on ______ seemed to be a piece of stone.
A. that B. which C. what D. it

【正确答案】 C
【答案解析】[解析] 宾语从句
[解析] 通读全句，不难发现该宾语从句仍缺主语，即空格处填入的词应充当从句的主语；经筛选，其余均不能用于引导宾语从句。