A、9小时
B、9<img width="13" height="37" src="http://admintk.100xuexi.com/UpLoadImage/2016-08-19/2c2638eb-a93f-4e1c-af70-4c888635b524.png" />小时
C、9<img width="13" height="37" src="http://admintk.100xuexi.com/UpLoadImage/2016-08-19/c21d1538-b509-4d0b-bff0-db05805f32aa.png" />小时
D、10小时