We arrived at work in the morning and found that somebody ________ into the office during the night．  [ ]

A．broke  

B．had broken

C．has broken  

D．was breaking

以初速度v₀竖直向上抛出一质量为m的小物块。假定物块所受的空气阻力f大小不变。已知重力加速度为g，则物块上升的最大高度和返回到原抛出点的速率分别为

A．和

B．和

C．和

D．和