is well known Hong Kong returned to China on July 1st 1997.A. It thatB. As /C. As a

问题补充：

is well known Hong Kong returned to China on July 1st, 1997.

A. It, that

B. As, /

C. As, as

D. It, which

答案：

A. It, that

B. As, /

C. As, as

D. It, which

解析：

it 为形式主语，其后的that从句为主语从句。