诗句“人间四月芳菲尽，山寺桃花始盛开”中的现象是什么原因造成的（　　）

①生命的意义不在于长短，而在于对人类社会所做的贡献     ②雷锋用实际行动诠释了生命的意义，延伸了生命的价值

③雷锋为人类留下了宝贵的精神财富                                         ④雷锋不珍爱自己的生命

小明用薄膜充水后制成水透镜模拟眼球中的晶状体，来比较正常眼、近视眼和远视眼的焦距大小．实验中测得甲图焦距为10cm，再将甲分别挤压成乙图、丙图的形状，并分别测量焦距，如图所示．

    It is said that about half of the people in China smoke. Many young boys and girls have the habit of smoking, though they are middle school students.
    More and more people have come to realize how serious this problem is. But they are never bored with it. ①Some people think it is a kind of fashion, some think it is of great fun and others think that smoking can relax themselves.
    Smoking causes many illnesses. A lot of people always cough(咳嗽)②______ ______smoking. The most serious illness caused by smoking is lung cancer. At the same time smoking is a waste of money. Beside, careless smokers may cause dangerous fires.
    It's known that smoking does harm to our health. We should get rid of(摆脱) the bad habit of smoking.