A:Where was it
B:Why was it
C:How was it
D:What was it
探究凸透镜成像规律时,小明在凸透镜前放一燃着的蜡烛,移动光屏并在光屏上找到清晰的像.然后将蜡烛远离透镜,调节光屏再次找到一个清晰的像,比较两像( )
下列所述的实例中,遵循机械能守恒的是 ( )
下列运算正确的是( )