问题补充：
is known to all that the Amber Room belongs to the Russians.
A. As
B. which
C. It
D. What
答案：
A. As
B. which
(答案→)C. It
D. What
解析：考查it用法。这里的it是形式主语，真正的主语是后面的that引导的主语从句that the Amber Room belongs to the Russians。句意：众所周知，the Amber Room属于俄罗斯。故C正确。
