阅读理解

　　The wind cause waves on the surface of the ocean and lakes．The wind transfers some of its energy to the water, through friction between the air molecules and the water molecules．Stronger winds cause larger waves like storm surges．You can make your own miniature waves by blowing across the surface of a pan of water．

　　Waves of water do not move horizontally(水平地), they only move up and down(a wave does not represent a flow of water)．You can see a demonstration of this by watching a floating buoy(浮标)bob up and down with a wave; it does not, however, move horizontally with the wave．

　　Tsunamis sometimes called tidal waves are different from surface waves; they are usually caused by underwater earthquakes, volcanic eruptions, or landslides．

　　What cause the tides?Tides are periodic rises and falls of large bodies of water．Tides are caused by the gravitational interaction between the Earth and the Moon．The gravitational attraction of the Moon causes the oceans to bulge(凸出)out in the direction of the Moon．Another bulge occurs on the opposite side, since the Earth is also being pulled toward the Moon and away from the water on the far side．Since the Earth is rotating(旋转)while this is happening, two tides occur each day．Isaac Newton was the first person to explain tides scientifically．

　　Spring tides are especially strong tides．They do not have anything to do with the season Spring．They occur when the Earth, the Sun, and the Moon are in a line．The gravitational forces of the Moon and the Sun both contribute to the tides．Spring tides occur during the full moon and the new moon．

　　Neap tides are especially weak tides．They occur when the gravitational forces of the Moon and the Sun are perpendicular(垂直的)to one another(with respect to the Earth)．Neap tides occur during quarter moons．

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阅读理解

　　Going to sleep may seem pretty boring compared with all the fun things there are to do while you're awake．But there's a lot going on in your mind and body while you're tucked under those covers．

　　Sleep, in fact, is as important to your survival as eating and drinking．Sleep improves your mood, makes you a better athlete, and helps you remember and understand what you learned during the day．During sleep your temperature drops．Your heart rate slows．Down goes the pressure of the blood moving through your veins．A chemical that controls growth(called a hormone)surges into your bloodstream．Scientists think sleep restores energy and improves your immune(免疫)system．We know what happens while we're asleep because scientists study volunteers who sleep in laboratories．The sleepers are hooked up to machines that measure brain waves, eye movements and muscle activities．

　　Sleep is like a school day：it's divided into different periods, or stages．When you're awake, your brain waves fire rapidly．As you begin to relax and drift into the first stage of sleep, your brain produces slower-moving waves and you lose awareness of your surroundings．As you slide to deeper sleep, your body repairs itself from the normal wear and tear of daily life．Then, as you begin to drift back up to a lighter sleep, your mind becomes more alert(机警), and your dreams begin．You're in REM sleep．

　　REM was names far the“rapid eye movement' that happens while you're dreaming．During REM sleep, your eyes move back and forth behind your timed lids, as though you were washing a movie．During other stages, you might move at that in bed, but during REM sleep you're still．That's probably because if you could move, your body would act out your dreams．As you get closer to morning, you spend more time in REM than in deep sleep, so you dream more．Researchers know that during REM sleep the part of the brain that handles learning and thinking is very active．

　　Getting too little sleep can affect your personality．Experts recommend that children get at least nine hours d sleep a night．So sleep fight．

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