A

    Skin­diving is a new sport today. This sport takes you into a wonderful new world. It is like a visit to the moon. When you are under the water, it is easy for you to climb big rocks, because you are no longer heavy.

    Here, under the water, everything is blue and green. During the day, there is plenty of light. When fish swim nearby, you can catch them with your hands.

When you have tanks of oxygen on your back, you can stay in deep water for a long time. But you must be careful when you dive in deep water.

    To catch fish is one of the most interesting parts of this sport.

    What's more, there are more uses for skin­diving. You can clean ships without taking them out of water. You can get many things from the deep sea.

    Now you see that skin­diving is both useful and interesting.

马克思说“俄国不花一文钱，不出动一兵一卒，而比任何参战国得到更多的好处”这一事件是（    ）

一块长方体的橡皮泥捏成一个正方体后，虽然它的形状变了，但它所占的空间大小没有变．