若两圆直径分别为4和6，圆心距为2，则两圆位置关系为（　　）

A．外离

B．相交

C．外切

D．内切

In order to finish the research, the professor always ______, for every day the light in his room didn't go

out until 4 a.m. [ ]

A. mixed up

B. cleaned up

C. turned up

D. stayed up