题目

There_________ three crayons and a pencil in the girl's pencil box. A . is B . are C . am D . be 答案：B起重机5 s内将2 t的货物由静止开始匀加速地提升了10 m高，取重力加速度g为10 m/s2，求此起重机应具备的最小功率.