A：地震时，山上的石块在下落过程中重力势能减小，动能增大，机械能增大
B：救灾的直升飞机保持一定高度水平匀速飞行并空投物资过程中，飞机机械能不变
C：直升飞机加速升空时，因螺旋桨转动在桨上下表面形成压强差使其所受升力等于重力
D：由于惯性，救援人员必须提前在飞机还未到达目标区域上方时投放物资
There is a new park near my house. My family often go to the park on the weekend. There aren't any tall buildings in the park. There is a big lake in the park. But we can't swim in the lake. There are many flowers and trees near the lake. There is a small hill behind the lake. Beside the lake, there is a small shop (商店). The park is beautiful. I like it very much.
如图所示动物体不同层次的结构中，属于器官的是（ ）
