城市或乡村提供的商品和服务功能主要由生产、流通、服务等产业部门来执行。这些部门要维持下去，必须赚得足够的收入来支付它的各项经营开支。我们把这种维持一家企业生存所需的最低人口数称为门槛人口。若甲、乙、丙均处在平原地区，且人口密度甲>乙>丙，则三个区域内级别相同的某商业职能部门的服务范围可能是(　　)

阅读下面一篇散文，完成后面小题。
                                                                         田埂上的精神
                                                                             张佐香
      麦子把田野的纽扣一粒一粒扣齐。但是，有一粒麦子被人们遗忘了，落在了田埂上，像一只浇了水后丢在堤上的桶。
      秋天继续深入。在清寒的晨气中，秋天的阳光抹在田野上，也抹在这一粒麦子上。它穿透土壤的黑暗，长出如针的小苗。来地里除草施肥的人们，自远方踏步而来，这一株麦苗兴奋地在微风中晃动着绿色的身子，似蝴蝶抖动金色的翅膀。然而，没有人在走近它时停下来，甚至没有闲暇望它一眼。因为田野里有大片的麦子，在等待着他们。
      本来它也应该生长在平整如砖的麦地呀！那儿有着它许许多多的兄妹，它们被调理得丰腴而肥硕。远远望去，它们宏大而又壮观。它们手挽手一起生长，一起成熟，一起走进农家的粮仓，与那些农民一起体验丰收的喜悦。田埂上只有一株孤零零的麦子，一株长错了地方的麦子。它很无奈。
      尽管这株麦子非常纤弱，但它长得非常卖力。它比田地里任何一株麦子都活得用力；它不想放弃自己生长的权利；它甚至还想用它那一片特别的绿，来引起人们的关注，从而获取生长所必需的元素。它大声地对每一位从它身边经过的人呐喊：“你们睁大眼睛瞧瞧！我不是一棵小草，我是麦子，我是一株麦子啊！”但是，没有人理会它。例外的一天，有个人偶然歇息时坐在它身边的田埂上，抽了一根烟，扔下烟蒂时瞅了它一眼，这时才突然记起来似的说：“噢，这儿还有一株麦子！”这时，麦子为有人记起它而高兴，它显得异常兴奋，甚至还有意地直了下它的身子，以便能让人看到它健康向上的样子。它不愿意让人笑话它，或者可怜它。那人只留下了些烟灰，拍了拍沾在裤子上的泥土，走了，就不再有踪影。
      这一株麦子已彻底为人们所遗忘，偶尔有小鸟落在它的身边，望着这深秋的大地一动不动。风吹，雨淋，日晒，它在孤独寂寞和无望中艰难地生长。它必须要生长，因为它是一粒落进泥土获得生命的麦子。它的存在属于大地，还有白云和高空飞翔的鸟儿，以及美好的黎明和黄昏。太阳格外地偏爱它，总是用暖暖的光芒映照着它的身子。
      尽管它是一株长在田埂上的麦子，被人们忽略，但它依然挚爱着这片土地和这片土地上的人们。它能体会到他们泥一脚水一脚跋涉于齐膝的泥淖中的滋味；它能感受到他们担着百余斤的担子压在肩上走上三四里地的分量。抢收抢种的季节，他们要在最短的时间内，顶着最毒的太阳，干着最繁重的活。他们受苦受累似乎是注定的。谁也没觉得不应该。想到此，它的身子一沉，似乎想把自己的根系伸进更深的土壤中，汲取更多的营养，使自己长得更健壮一些。
      冬去春来，它终于开始抽穗，并且呈现出金黄的颜色。当一位农人收割了无数麦子后，发现了它，欢喜得了不得，小心翼翼地割下这株麦子，把它捧在手心，喃喃地自言自语：“麦子，田埂上也能长出这么好的麦子，它承的是天惠呀！”
     一颗明亮而智慧的种子，只要根植于泥土，它就能结出果实，正如这田埂上的一株麦子。它生长的是田埂上的精神。

    Why do people travel? There are many reasons one can think of when asked questions like this.

    To travel far enough to meet yourself

    Sometimes you find yourself in the middle of nowhere. ____ You find out your abilities. When you are offered a different lifestyle, you can find out what you are made of. The farther you go from your home, the nearer you come to your true self.

    ____

    If you look back at all the amazing memories of your life, you will realize that most of them were out of your comfort zone. Traveling is dangerous, full of life threatening possibilities and will not always be comfortable, but at the same time, it gives irreplaceable memories.

    To slow down and relax

    A wise man once said that never get so busy making a living that you forget to make a life. Money is worth nothing if you cannot spend it on a little adventure. While we are deeply involved in making money, we forget that time is going through our fingers. ____ The feeling of being away from your workplace is pure happiness. The feeling of not having to worry about the never ending piles of files is pure joy. ____

    To celebrate life

    Life is short and the world is wide. One day you might wake up and realize that you don't have time to do everything that you have always wanted to do, anymore. Once in a while, make time to appreciate the fact that you are alive, young, free and healthy. ____

A. To break through your comfort zone.

B. To become a storyteller.

C. Escape life for a little while because experience is far more valuable than money.

D. You can relate to the world and connect to others.

E. And the feeling of being away from your boss for a few days is pure pleasure.

F. So, go traveling to celebrate life itself.

G. Traveling lets you discover yourself.