题目

We         at the suggestion to improve our plan by the school girl then. A．have amazed                                              B．have been amazed C．had been amazed                                        D．were amazed 答案：D如图所示，用方向不变的力F，将杠杆从A位置匀速提升到B位置的过程中，F的大小变化情况有（　　） A、保持不变B、逐渐变小C、逐渐变大D、先变大再变小