关于平抛运动，下列说法中正确的是 ( )

A．平抛运动的轨迹是曲线，其速度方向和加速度方向可以在同一条直线上

B．平抛运动是一种匀变速曲线运动

C．平抛运动的水平射程s仅由初速度v₀决定，v₀越大，s越大

D．平抛运动的落地时间t由初速度v₀决定，v₀越大，t越大

Not until they left school _____ how much their teachers loved them and helped them. [ ]

A. they realized

B. did they realize

C. they would realize

D. had they realized