The light from the campfire brightened the darkness, but it could not prevent the damp cold of Dennis's Swamp (沼泽地) creeping into their bones. It was a strange place. Martin and Tom wished that they had not accepted Jack's dare. They liked camping, but not near this swamp.

    “So,” Martin asked as they sat watching the hot coals. “How did this place get its name ? ”

    “Are you sure you want to hear it ? It's a scary story,” warned Jack.

    “Of course!” cried out Tom. “If there were anything to be scared of, you wouldn't have chosen this place!”

    “Ok, but don't say I didn't warn you,” said Jack, and he began this tale.

    “Way back in time, a man called Dennis tried to start a farm here. He built that cottage over there to live in . In those days, the area looked quite different — it was covered with tall trees and the swamp was a crystal-clear river. After three hard years, Dennis had cleared several fields and planted crops. He was so proud of his success that he refused to listen to advice.

    “ 'You are clearing too much land, ' warned one old man. ' The land is a living thing. It will hit back at you if you abuse it. '

    “ ' Silly fool,' said Dennis to himself. 'If I clear more land, I can grow more crops. I'll become wealthier. He's just jealous!'”

    “Dennis continued to chop down trees. Small animals that relied on them for food and shelter were destroyed. He was so eager to expand his farm that he did not notice the river flowing slowly towards his door. He did not notice salt seeping to the surface of the land. He did not notice swamp plants choking all the native plants.”

    “What happened? ” Martin asked. It was growing colder. He trembled, twisting his body closer to the fire.

    “The land hit back ---- just as the old man warned, ” Jack shrugged. “Dennis disappeared Old folks around here believe that swamp plants moved up from the river and dragged him underwater. His body was never found.”

    “What a stupid story, ” laughed Tom. “Plants can't …” Before he had finished speaking, he screamed and fainted (晕倒). The other two boys jumped up with fright, staring at Tom. Suddenly, they burst out laughing. Some green swamp ivy (常春藤) had covered Tom's face. It was a while before Tom could appreciate the joke.

与环境人口容量呈负相关的因素是（   ）

课外阅读：阅读下面文字，完成下列问题。

听 泉

    演奏《二泉映月》，有一种心灵沐浴冲凉的感觉。琴弓的马尾吃住了弦，像是把山里的玉石锯开了一个小缝儿，泉水呢顺着左手指头尖儿款款流出来，跌扑回环绕在身边。心里所有的浮躁、郁闷、烦琐，都被淙淙流泉冲走了。身上清爽得很、干净得很。舌根也甜润润湿漉漉。说来真的感谢盲人音乐家阿炳（华彦钧），他用一把胡琴，教会了我们听泉。让我们知道感觉山中清泉，应该打通生命所有孔窍，只凭眼睛直观是不够的。是啊，古人说刑天舞干戚，以乳为目，以脐为口，就是说人的浑身上下都生着精明的器官，人本来就是精灵剔透的灵长目，我们和炳哥的差别就在于不懂得让心灵长出眼睛看宇宙，让耳朵生出触须抚摸自然，从这个角度说，也许我们才是真正的“盲人”。还有，我们没有化清流为音乐的神力，在盲人音乐家阿炳这里，泉水是灵感的婴儿。他一下子就捕捉住了稍纵即逝的灵感，再加进了自己的天分、才情与生命感悟，人间就淌出了不朽的经典，音乐的清泉——《二泉映月》。

     “二泉”从前只是穷道士沿街卖艺的一支曲子，如果不是遇到杨荫浏先生，那音乐的“泉水”不知会在哪儿幽咽断流了。我在音乐学院学琴的时候，老先生杨荫浏的学养和人品极为师生尊崇。杨荫浏与阿炳之间的理解与默契，是人间知音的绝唱，俞伯牙与钟子期也不能相比。换句话说，琴师俞伯牙倘若遇到杨荫浏，就大可不必因世无知音摔碎瑶琴了。杨荫浏是在建国初期为抢救濒临灭绝的文化遗产，寻访阿炳的。背着笨重的录音机，他和阿炳谈心、谈艺、谈琴。用那时候流行的“履带”般的录音机带，录下了阿炳的曲子。这首曲子无题，阿炳让杨先生取个题目，杨先生思忖了片刻说，就叫做《二泉映月》吧。

    可以想象这时候阿炳是多么感动和惊奇，他那深陷的眼窝红了，几乎要流出“泉水”了，面前这位先生不仅听懂了他，把他的琴声录下来，让他的音乐永远活着，而且，一语点睛，戳动了他的心泉之门。是啊是啊，这娓娓动听的音乐，不是映月的天下第二泉又是什么？泉水一冲出深山罅隙，月光就扑了过来。一轮梨花月变成了液体。揉碎了月光，叮叮咚咚唱着歌，奔跑跳跃在惠山的绿竹林青草地。忽然从高高的石崖向下“蹦极”，珠玉四溅；忽然在花丛间潜伏蛇行，若断还连，幽幽咽咽的；忽然又在光滑的鹅卵石溪床上跳着轻松的舞步，带着小鱼，携着蝌蚪，跑向山外的世界……音乐在胡琴的三个把位回还，如曲水流觞。装饰音和滑音机智乖巧，似鱼戏水草。斗弓细碎流畅，清流里有诉不尽的柔情。《二泉映月》是回旋曲式，让人把醉人醴泉回味品咂个够。更要紧的是，杨先生听着盲人音乐家心泉的律动，深深感觉到了阿炳对生命和自然的热爱，也听到了涌动的泉水里，有一点淡淡的哀伤。

    阿炳和杨荫浏都已经离我们远去了，可映月的二泉还奔涌在我们的生命和生活中。记得这首美妙绝伦的乐曲使著名指挥家小泽征尔由衷倾倒，他说过，《二泉映月》应该跪下来听。是的，此曲只应天上有，人间哪得几回闻？也许，惟有双膝跪倒，才可以聊表心中的虔敬与感激。我们感激创造美的阿炳和发现美的杨荫浏。阿炳开掘出了他心中独一无二的音乐泉，杨荫浏牵着“泉水”的手，出了山。

【注】华彦钧（1893—1950）现代民间音乐家。小名阿炳，江苏无锡人，出身贫寒，做过道士和吹鼓手，后沦为流浪艺人。传谱有二胡曲《听松》《二泉映月》琵琶曲《昭君出塞》《大浪淘沙》等。