A:鸡会辨认食槽
B:老鼠拉杆取食
C:蚯蚓走迷宫
D:老母鸡抚育小猫
I saw him in the library yesterday. He ________ a book at that moment.
①如图所示,F1是作用在抽水机手柄A点处的动力,O为支点。请画出动力F1的力臂L1和B点处所受的阻力F2
②如图所示,为了使轻质杠杆AB在如图所示位置静止,请在杠杆上画出所施加最小力F的示意图及其力臂L
③请根据实物电路,在右边方框内画出电路图