在工程竣工验收后建设单位应及时收集勘察、设计、施工和监理单位的档案资料，在（）内将工程档案资料移交城建档案馆。

A.1个月

B.2个月

C.3个月

D.6个月

Gold which is 10 Karats in proportion ______ in the U.S.

A．represents the highest grade of gold

B．cannot be sold

C．never carries a Karat quality mark

D．represents the lowest-grade gold marketable