From the dates__________on the gold coin, we decided that it was made five hundred years ago.

A．marking

B．marked

C．to be marked

D．having been marked

我国洁净室室内发尘量是以（）计算的。

A.每平方米发尘量地板面积

B.每人每分钟发尘量

C.单位容积发尘量

D.各尘源发尘量之和