單項選擇題恒定流具有下述哪種性質(zhì)()?

A.當?shù)丶铀俣?img src="https://newimg.ppkao.com/2015-10/liuziyi/2015102714461030769.jpg" />u/t=0
B.遷移加速度u/s=0
C.當?shù)丶铀俣?img src="https://newimg.ppkao.com/2015-10/liuziyi/2015102714461030769.jpg" />u/t≠0
D.遷移加速度u/s≠0