王强参加一长3000米的跑步，他以6米/秒的速度跑了一段路程后，又以4米/秒的速度跑完了其余的路程，一共花了10分钟，他以6米/秒的速度跑了多少米？设以6米/秒的速度跑了x米，列出的方程是 _________ ．

He failed in the driving test again. He _____. [ ]

A. must have disappointed

B. must have been disappointed

C. might be disappointed

D. couldn't be disappointed