某物体同时受到两个在同一直线上的力F1、F2的作用,物体由静止开始做直线运动,其位移与力F1、F2的关系图像如图所示,在这4m内,物体具有最大动能时的位移是( )
A:1m
B:2m
C:3m
D:4m
Yesterday, I came across my former classmate, but his name ________ me, which made me embarrassed.
温室大棚栽培蔬菜时,夜间常常适当降低大棚内的温度,其最主要的目的是( )