—I usually watch TV till 11 o’clock in the evening.

—Really ? Are you __________?

A．allowed to stay up

B．allow to stay up

C．allowing staying up

D．allowed stay up

某单位某月1~12日安排甲、乙、丙三个值夜班，每人值班4天。三人各自值班期数字之和相等。已知甲头两天值夜班，乙9、10日值夜班，问丙在自己第一天与最后一天值夜班之间，最多有几天不用值夜班？

A.6 

B.4 

C.2 

D.0