阅读理解

    The African elephant, the largest land animal remaining on earth , is of great importance to African ecosystem(生态系统). Unlike other animals, the African elephant is to a great extent the builder of its environment. As a big plant-eater, it largely shapes the forest-and-savanna(大草原)surroundings in which it lives, therefore setting the terms of existence for millions of other animals that live in its habitat(栖息地).

    It is the elephant's great desire for food that makes it a disturber of the environment and an important builder of its habitat. In its continuous search for the 300 pounds of plants it must have every day, it kills small trees and underbushes, and pulls branches off big trees. This results in numerous open spaces in both deep tropical forests and in the woodlands that cover part of the African savannas. In these open spaces are numerous plants in various stages of growth that attract a variety of other plant-eaters.

    Take the rain forests for example. In their natural state, the spreading branches overhead shut out sunlight and prevent the growth of plants on the forest floor. By pulling down trees and eating plants, elephants make open spaces, allowing new plants to grow on the forest floor. In such situations, the forests become suitable for large hoofed plant-eaters to move around and for small plant-eaters to get their food as well.

    What worries scientists now is that the African elephant has become an endangered species. If the elephant disappears, scientists say, many other animals will also disappear from vast areas of forest and savanna, greatly changing and worsening the whole ecosystem.

①单基因遗传病中的显性遗传病

②染色体遗传病

③单基因遗传病中的隐性遗传病 

④性染色体病．

两棵树

墨村

       ①胖子和瘦子那时候很年轻，结伴到山里去，在一风景绝佳处，游兴正浓的胖子和瘦子同时发现了一种很奇特的树。两人生性好抬杠，各持己见，互不相让。胖子说，这树肯定能长成栋梁之材！瘦子说，那不一定。胖子说，咱各弄一棵树苗试一试！瘦子说，那就弄吧。

       ②于是，胖子和瘦子两家的庭院里便都有了这种树，只不过胖子栽在地上，瘦子植在瓦盆里。他们较着劲儿为各自的树苗儿浇水、施肥、松土、修剪。日子一晃悠，胖子头顶秃了，瘦子脑袋光了。

       ③胖子的树长得有一搂粗细，铜杆铁臂，挺拔巍峨，冠盖如伞，遮天蔽日。胖子笑眯眯搔着脑壳对瘦子说，咋样，不错吧？

       ④瘦子的树虽只一米有零，且疙疙瘩瘩，歪歪扭扭，枝丫纤弱，却被瘦子侍弄得盘龙虬扎道骨仙风，随便站在哪个角度上看，都能让人陡生一种云天雾地深奥难测之感。

       ⑤一日，被一采风的摄影记者撞见，记者被其别有洞天的玲珑奇绝与怪诞飘逸的鬼斧神工所深深折服，惊叹之余，“叭叭叭”一口气拍完了整卷胶卷。月余，一封来自首都北京的牛皮大信径送瘦子家，竟是那位记者寄给他的一份画报。瘦子一蹦三尺高，乖乖，咱的大名咱的树竟上了《人民画报》咧！瘦子笑眯眯哗啦啦地抖着画报对胖子说，咋样，不错吧？

       ⑥胖子撇撇嘴，熊样儿，烧火都嫌碍事！瘦子吊吊眉，整形，谁愿跟你换！

       ⑦忽一日，县里来辆卡车，从车里跳下一个瘦猴样的人，要出大价钱买胖子这棵树。胖子头摇得如拨浪鼓，冲着在门口晒暖的瘦子夸张地扯着嗓门吼，啥？你说啥？九百？不中不中，再添五十也不卖。

       ⑧最后，那人阴着脸甩出十张领袖票，吃亏似的连树根都挖出来拉走了。那几日，胖子红光满面，进出家门，嘴里都韵味十足地老哼着“包龙图我打坐在开封府……”

       ⑨又一日，市里来辆轿车，从里面钻出一个弥勒佛样的人，操着一口普通话嚷嚷着要找瘦子。胖子自告奋勇领那人来到了瘦子家。那人一进院门就被瘦子的那棵树惊得老半天都没合上张大了的嘴，他激动地一边搓手一边连声地嚷：“名不虚传！名不虚传！”

       ⑩那人毕恭毕敬地朝瘦子直擩过滤嘴烟：“早闻其名，如雷贯耳，今日得见，真是三生有幸啊！不知道您老舍不舍得忍痛割爱，这个数送给小辈，咋样？”那人迫不及待地伸出了一只手掌。瘦子耷拉下眼皮，抽出了自己的旱烟袋。那人忙又加上了另一只手掌的三个指头。

       ⑪一旁的胖子急得不行，朝着瘦子直嚷，你你你，你神经病啊，八十了你还不卖？瘦子睁开眼，不紧不慢地往烟锅里装着旱烟丝，冲那人懒懒一笑，你是内行，呵，给两个巴掌不多吧？你说。那人一愣，随之点头如捣蒜，啊，您老说得对，是不多，是不多！

       ⑫乖乖，这东西也值一百？胖子一声惊叫。瘦子鄙夷地哼了一声。

       ⑬多了，还是少了？胖子一脸问号。瘦子白了丈二和尚般的胖子一眼，沉默良久。瘦子突然一磕烟袋锅，声音朗朗地对那人说，成，就冲你刚才的那句掏心窝子的话，九千八你赶紧搬走吧，免得一会儿我后悔了……

       ⑭那人受宠若惊点头哈腰喜出望外，在滚圆肚子下边的钱袋里掏钱的手都激动得颤抖不已。临走，从车上拿出一条烟往瘦子怀里塞。

       ⑮胖子愕然。

       ⑯两棵树没有了，胖子和瘦子心里都空落落的没了根底，再见面时，你望望我，我看看你，再也激不起打赌的欲望了。

下列各句中，没有语病的一句是（）