下列属于哺乳动物的是（　　）

设m，n是两条不同的直线，α，β，γ是三个不同的平面，给出下列四个命题：

①若m⊥α，n∥α，则m⊥n   

②若α∥β，β∥γ，m⊥α，则m⊥γ

③若m∥α，n∥α，则m∥n  

④若α⊥γ，β⊥γ，则α∥β

其中正确命题的序号是（　　）

阅读下文，完成文后题目。
                                                                                                                      我看到了一条河
        童年在我的记忆中比较模糊，但其中有几个片段却令我记忆犹新。
        我4岁那年，有一次，妈妈开车带我回家。路上，她让我在离家几英里（1英里约合1.6公里）的农田边下车，然后自己找回家。虽然那次以我彻底迷路而告终，但此事对我影响很大。在这样的环境中，我从小就乐于寻找挑战。
        刚开始学游泳时，我大概有四五岁。我们全家和朱迪斯姑姑、温迪姑姑、乔姑父一起在德文郡度假。我最喜欢朱迪斯姑姑。她在假期开始时和我打赌，如果我能在假期结束时学会游泳，就给我10先令（先令是英国旧币，10先令相当于半个英镑）。于是我每天泡在冰冷的海浪里，一练就是几个小时。但是到最后一天，我仍然没有学会游泳。我最多只能挥舞着手臂，脚在水里跳来跳去。
      “没关系，里克，” 朱迪斯姑姑说，“明年再来。”
        但是我决心不让她等到下一年，再说我也担心明年朱迪斯姑姑就会忘了我们打赌的事。从德文郡开车到家要12小时。出发那天，我们很早起身，把行李装上车，早早地启程了。乡间的道路很窄，汽车一辆接一辆，慢吞吞地往前开。车里又挤又闷，大家都想快点儿到家。但是，这时我看到了一条河。
       “爸爸，停一下车好吗？”我说。这条河是我最后的机会，我坚信自己能赢到朱迪斯姑姑的10先令。“请停车！”我大叫起来。爸爸从倒车镜里看了看我，减慢速度，把车停在路边的草地上。
      “里克看见一条河，”妈妈说，“他想再试一次游泳。”
      “可我们不是要抓紧时间赶路吗？”温迪姑姑抱怨说，“我们还有很长一段路程呢！
      “温迪，给小家伙一次机会嘛，”朱迪斯姑姑说，“反正输的也是我的10先令。”
        我脱下衣服，穿着短裤往河边跑去。我不敢停步，怕大人们改变主意。但离水越近，我越没信心，等我跑到河边时，自己也害怕极了。河面上水很急，发出很大的声响，河中央一团团泡沫迅速向下游奔去。我在灌木丛中找到一处被牛踏出的缺口，趟水走到较深的地方。爸爸、妈妈、妹妹琳蒂、朱迪斯姑姑、温迪姑姑和乔姑父都站在岸边看我的表演。女士们身着法兰绒衣裙，绅士们穿着休闲夹克，打着领带。爸爸叼着他的烟斗，看上去毫不担心。妈妈一如既往地向我投来鼓励的微笑。
        我定下神来，迎着水流，一个猛子扎了下去。但是好景不长，我感到自己在迅速下沉。我的腿在水里无用地乱蹬，急流把我冲向相反的方向。我无法呼吸，呛了几口水。我想把头探出水面，但四周一片空虚，没有借力的地方。我又踢又扭，然而毫无进展。
        就在这时，我踩到了一块石头，用力一蹬，总算浮出了水面。我深吸了口气，这口气让我镇定下来，我一定要赢那10先令。
        我慢慢地蹬腿，双臂划水，突然我发现自己正游过河面。我仍然忽上忽下，姿势完全不对，但我成功了，我能游泳了！我不顾湍急的水流，骄傲地游到河中央。透过流水的怒吼声，我似乎听见大家拍手欢呼的声音。等我终于游回岸边，在50米以外的地方爬上岸时，我看到朱迪斯姑姑正在大手提袋里找她的钱包。我拨开带刺的荨麻，向他们跑去。我也许很冷，也许浑身是泥，也许被荨麻扎得遍体鳞伤，但我会游泳了。
      “给你，里克，”朱迪斯姑姑说，“干得好。”我看着手里的10先令，棕色的纸币又大又新。我从没见过这么多钱，这可是一笔巨款。
        爸爸紧紧地拥抱了我，然后说：“好了，各位，我们上路吧！”直到那个时候，我才发现爸爸浑身透湿，水珠正不断地从他的衣角上滴下来。原来他一直跟在我身后游。                       

    Garbage(垃圾) Island

    You can't see it from the air. It's almost impossible to see from a ship. But somewhere in the North Pacific is a huge island of garbage, just below the water surface.

    What is the island made of?

    The garbage island is not an island, but a collection of millions of plastic and other objects. The water movements of Pacific Ocean bring the objects together and cause them to go around in a big circle.

    Charles Moore found it in 1997 and named it “the Great Pacific Garbage Patch” .

    Where does all the plastic come from?

    Much of the garbage comes from everyday objects, such as shopping bags and water bottles. Some of these objects finally reach the ocean. Garbage from the western coast of North America takes about six years to reach it. Objects from East Asia take about a year. Other garbage comes from ships passing through the area.

    Is the Garbage Patch dangerous?

    The larger pieces of garbage are a problem for wildlife. For example, sea turtles（海龟）and seabirds often think the plastic is their food. They eat the plastic and die.

    In addition, the plastic stops sunlight from reaching deeper water. Without sunlight, very small sea animals die. Then, there is less food for larger fish to eat.

    What can we do to help stop it?

    Cleaning up the island isn't easy. But we can make people realize the problem. One environmentalist(环保主义者), David de Rothschild, is sailing around the world in boat made of plastic bottles to teach people about the problem of garbage in the sea.

    Another idea is that we can recycle the plastic garbage. Environmental engineer Cesar Harada is building a robot that collects pieces of plastic. Harada hopes to use his robot in the Pacific. Harada also has a website for reporting environmental problems. He says, “I hope everybody can become an environmental activist.”