内部关系，是指公安机关内部上下级之间、同级与同级之间、警种与警种之间，按照( )构成的关系。

A．职务高低

B．级别不同

C．一定规则

D．警衔高低

The large size and roughly circular shape of the Pacific made some scientists think that it （） a hole left when the moon separated from the earth.

A. used to be

B. would have been

C. might have been

D. should have been