We are at your service. Don’t ________ to turn to us if you have any further problems.

A．beg

B．hesitate

C．desire

D．seek

水滴从屋檐上自由落下，经过高度为1.8m的窗户，历时0.2s，若不计空气阻力，g取10m/s²，求屋檐离窗顶的高度和水滴落到窗底的速度大小。