There ____________ some milk in the fridge a moment ago.[ ]
A. are
B. was
C. were
答案:B
压缩的弹簧释放将球弹起,球升至最高点,如图所示.在甲到乙的过程中,弹簧的弹性势能________ ,小球的动能________ ;乙到丙的过程中,小球的重力势能________ (选填:变大/变小/先变大后变小/先变小后变大) .