题目

 ----- Mary looks very upset. She _______ failed to pass the exam.    ----- I guess so. It's very difficult after all.     A must have   B could have   C should have  D might have 答案：A如图所示，在光滑水平面上有A、B两球，中间连一弹簧，A球固定，今用手拿住B球将弹簧压缩一定距离，然后释放B球，在B球向右运动到最大距离的过程中，B球的加速度将__________，B球的速度将__________，弹簧的弹性势能将____________．