All his attention________on the computer game he was playing,so he even didn't notice his mother

enter the room. [ ]

A. has been fixed

B. was fixing

C. was fixed  

D. fixed

一辆摩托车行使的最大速度为108km/h。现让摩托车从静止出发，要求在4min内追上前方相距1km,、正以25m/s的速度在平直公路上行驶的汽车。则该摩托车行使时，至少应有多大的加速度？