A:/; the
B:the; /
C:an; the
D:the; a
人在游泳时,使人前进的力是( )
— Yes, I like it very much, ________ it's not good for health.
①两摆球在最低点的速度大小相等
②两摆球在最低点对悬线拉力大小相同
③两摆球在最低点加速度大小相等
④两摆球在最低点动能相等.