单选题 ______ is well known ______ Hong Kong returned to China on July 1st, 1997.
   A) It, that          B) As, /C) As, as              D) It, which
【正确答案】 A
【答案解析】it为形式主语，其后的that从句为主语从句。比较下面一题，答案选B。