下列实验操作中，正确的是（　　）

达尔文认为，生物进化的原因是（    ）

    I was in my first year of college, making friends and enjoying life, but then my whole world turned upside down. I had a heart attack. It felt like someone was stabbing (刺) me in the chest with a knife over and over again.

    After three months of rest I went back to college, but then things took a turn for the worse. I was staying at my Nana's house and woke up in the middle of the night with a terrible pain in my chest. I knew I was having a heart attack again.

    I couldn't even shout for help. Luckily my grandpa was going to the toilet and heard me falling out of bed. If it wasn't for him, I probably wouldn't be here.

    The two holes in my heart were causing the problems and I needed an operation immediately to repair them. Unfortunately, the surgery didn't go well and they only managed to repair one of the holes.

    When I woke up from the operation, I had a really dry mouth and couldn't wait to have something to eat and drink. The biggest shock of all came when I was told that I needed a heart transplant and was put on the register. The doctors were stunned at how quickly heart failure came on – it usually takes years, but it took my heart less than six months to get to that stage. My whole world came crashing down, but I stayed strong. It was a choice between crying every day and getting on with my life.

    As time went on, life became even harder. I hated feeling weak all the time and needing help with everything. It got to the point where I thought I would never get a new heart. I was diagnosed with depression.

    Even though I thought that Christmas 2008 would be my last, I really enjoyed it and even had a good New Year. Everyone was crying for me when the clock struck midnight and they told me to keep fighting.

    A week later, I got a call from the doctors saying they'd found a suitable donor (捐赠人). My wish came true and thankfully the operation went well. I spent four hours in surgery where they took out my old heart and put a new one in. When I woke up I burst out crying. I had a second chance at life.

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                                                                                                                陕北的山

                                                                                                                 祁玉江
        ①陕北真是一个神奇而美妙的地方。说它神奇而美妙，并不只是因为它的地下埋藏了多少石油、煤炭、天然气等富集的矿产资源，也不只是因为它的地上盛产了多少瓜果梨枣、五谷杂粮等绿色食品，更不只是因为生于斯长于斯的那些纯朴善良的山民们和世世代代涌现出的英雄人物，而更多的则是因为它的山——神奇而美妙的陕北的山!
        ②我常常怀疑造物主将世界上所有的山都堆在了地球的这一隅，使陕北成了山的世界、山的海洋!抬头是山，低头也是山；吃的是山，住的还是山。山是生存在这片广袤大地上的人们的物质和精神寄托，是取之不尽、用之不竭的生命源泉。
        ③我生在陕北，长在陕北，曾经和陕北的山零距离地亲吻过。在这茫茫的大山深处，我扶过犁，拾过粪；吞过糠，咽过菜；淌过汗，流过泪。一切都是那么无助，那么渺茫。我对生我养我的陕北的山，鄙视过，厌倦过，一度竟然埋怨起我的祖先为什么不把自己定居在广阔的平原上、浩瀚的大海边、秀丽的江南间，而偏偏要将家安在这贫瘠清苦偏远落后的千山万壑中，使得日后的子孙们在这里永远地受苦受难，千回百转走不出大山，享受不到山外精彩世界的生活!我甚至怨恨大山，诅咒大山，盼望有一天天崩地裂，将这茫茫大山夷为平地；或者乞求上苍有朝一日将这些绵绵山峦搬到天的尽头，使这里的人们再也不要受苦受难了。
        ④但是现在想来，我那时是多么的无知，多么的任性，多么的忘本!如果当初没有汲取大山的营养，没有经过大山的磨砺，没有遵循大山的教诲，我不可能体格健壮、意志顽强，更不可能走出大山。
        ⑤当你登上高高的山巅，举目四望，视野所及，苍苍茫茫，一望无际。那数不清的梁峁，千姿百态，形状各异，像条条巨蟒，像只只雄狮，像头头大象，像个个巨人……盘踞在这广袤的黄土高原上，正蓄势待发。那层峦叠嶂的山脉，仿佛是大海的波涛，一浪接着一浪，汹涌不退，大有排山倒海之势。总之，任凭你怎么想象，想象什么就是什么。
        ⑥陕北的山胸襟开阔，无私无畏，可以容纳世界的一切，包容人间万象。如果你走错了路，做错了事，它并不记恨你、抛弃你，依然像慈祥的母亲一样，紧紧地把你揽在怀里，教育你、鼓励你、引领你重新振作精神，在人生的道路上继续前进。夜晚，睡在大山里就像睡在慈母的怀抱一样，是那样的温馨，那样的甜蜜。
        ⑦如果你坐在高高的山巅，细细地观察，认真地品味，这广袤的高原就像一泓清澈的湖水，一尘不染。没有喧闹，没有嘈杂，一片寂静，远处偶尔传来几声鸡鸣、狗吠、鸟叫、机器声，升腾起几缕袅袅炊烟，使空旷寂静的大山显得更加静寂。如果你疲惫了，烦恼了，不妨走进大山，走上这高高的山梁，在那儿坐一坐，歇一歇，躺一躺，吸一吸清新的空气，接受一下山风的抚摸，你的精神会顿时为之一振，心灵得到了净化，一切疲倦和烦恼早已抛到九霄云外，蓦然有一种返璞归真的感觉。
        ⑧我忽然明白了，陕北这块贫瘠的土地上，为什么走出了像李自成、刘志丹、谢子长这样的无数英雄豪杰和革命志士；为什么产生了那么多悲欢离合的动人故事和百唱不厌的像《走西口》、《东方红》等信天游歌曲；为什么***主席将长征的落脚点、抗日战争的出发点、解放战争的总后方选在了陕北，而且在这里一住就是13年；为什么陕北人是那样的豪放，那样的纯朴，那样的勤劳，那样的坚强!