题目

Iin the exam, but I was too careless. A . should have been careful B . must have been careful C . should be careful D . must be careful 答案：A一个小朋友从滑梯上匀速滑下的过程中，下列说法正确的是（ ）A．动能减小，重力势能减小，机械能减小B．动能不变，重力势能减小，机械能减小C．动能减小，重力势能增大，机械能不变D．动能不变，重力势能减小，机械能不变