使用下列简单机械费力的是（ ）
A：钢丝钳
B：起重机的动滑轮
C：赛艇的桨
D：扳手
The students are required by the teacher________ more attention to their handwriting.
甲、乙、丙三人骑自行车匀速行驶，甲在1h内行驶15km；乙在3min内行驶750m；丙行驶100m需24s；则三人骑车速度的快慢为（ ）
