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10。Another wonderful story is that of Journey to the Center of the Earth。
《地心之旅》是他的另一个优秀的故事。
that在句中为代词，代指 the story。英语中有时为避免重复常用one或that来代指前面提到过的人或物。one为泛指想当于a＋sth。，有时前面有the或某些形容词修饰；that相当于the one，一般表示特指。
I don’t like the red coat； I like the yellow one。 我不喜欢那件红的，我喜欢那件黄色的大衣。
A bridge made of stone is always stronger than one made of wood。=A bridge made of stone is always stronger than a bridge made of wood。
The bridge stone made of is always stronger than that made of wood。=The bridge made of stone is always stronger than the bridge made of wood。 石头建造的桥一般比木头建造的桥结实。
UNIT 13 The water planetTHE PROPERTIES OF WATER 水的性质
Earth is an ocean planet。 About three billion years ago； life on our planet began in the deep blue seas。 99％ percent of the living space on earth is in the oceans。 Marine life is incredibly rich and varied。 There are about five million species in the oceans and we have yet to learn much about them。 Life in the oceans ranges from the tiniest plants all the way up to giants like sharks and whales。 What is it that makes the ocean such a great place to live？ The answer is water。
地球是个水球。大约三十亿年前，地球上的生命从海洋深处诞生了。地球上大约99％的生存空间都在海洋里。海洋生物的丰富和多样性超乎想象。海洋里有五百多万种生物，其中很多还需要我们去加以了解。海洋里的生物从微小的浮游生物到庞大的动物如鲨鱼和鲸鱼都有。到底是什么使得海洋成为这么好的生活环境？答案便是水。
CHEMICAL STRUCTURE 水的化学结构
The chemical structure of water makes it an excellent medium for life。 Water is actually quite simple； but the way the water molecule is formed gives water its unique properties。 The water molecule is made up of two hydrogen atoms and one oxygen atom。 The two hydrogen atoms form a polar molecule； that is； one with a slightly positive end and one with a slightly negative end。 The chemical structure of water also makes it different from almost everything else on earth。 Water is a liquid at room temperature and has a relatively high freezing point。 Because water is polar； it can break down or dissolve both solids and gases。 The nutrients in whatever falls into the ocean will quickly become available to other living creatures。
水的化学结构使得它成为生命存在的奇妙的载体。水的构成实际上很简单，但是水分子的构成方式使得水具有独特的性质。
水分子是由两个氢原子和一个氧原子构成的。
两个氢原子组成了一极，也就是说，水分子的一端弱微呈阳性，另一端弱微成阴性。水分子的这种结构使得它成为地球上独一无二的东西。在室温下；水呈液态，并且有相对较高的结冰点。因为水具有两极性，水无论是呈固体还是气体都可以分离（分解）。流入海洋里的任何营养物都会马上被其他的生物吸收。
SALINITY 水的盐度
When dissolved gases and solids mix with pure water； the result is sea water； or salt water。 The salinity of the earth’s oceans is about 35 parts per thousand； meaning that there are about thirty…five grams of dissolved solids and gases in one kilo of water。 Even though the pure water is what gives sea water its main properties； the salinity of sea water affects both its weight and freezing point。 Salt water has a lower freezing point and is heavier than pure water。
当分解后的气体和固体和纯水混合后，水就成了海水或盐水。地球海洋的盐度是千分之三十五，也就是说大约一千克的水中就会有35克的已容固体或气体。即使纯水使海水具有了水的主要性质，但海水的盐分也会影响它的比重和冰点。盐水的结冰点较低，比重也比淡水大。
DENSITY 密度
Density is the relationship between mass and volume and is measured in kilos per cubic meter （kg/m3）。 The density of pure water is 1；000kg/m3； meaning that one cubic meter of water weighs one thousand kilogram。 If a substance has a higher density； say 5；000kg/m3； it will not float on water。 Marine animals and plants take advantage of the density of water。 With the right kinds of body； it is possible to heat around in the ocean and let the water do the work。 When water freezes； its density decreases。 If it didn’t； the oceans would be frozen solid。
密度是质量和体积之间的关系，通常用每千克/立方为测量标准。纯净水的密度为1000kg/m3；也就是一立方米水的重量为一千公斤。如果某种物质的密度比较大，比如说为5000kg/m3，它就不会漂浮在水上。海生动植物利用了海水的密度。由于生物有合适的体型，它们能够自由地漂浮在海洋之中，海水能帮助它们。当水结冰时，它的密度会降低。如果不是这样的话，海洋就会凝固成固体。
HEAT CAPACITY 水的热容量
Heat capacity is the amount of energy it takes to raise the temperature of a substance one degree centigrade。 The heat capacity of water is relatively high。 Water can absorb and give off a lot of heat without big changes in its temperature； thus creating a stable environment。 Most animals and plants are sensitive to large or sudden changes in temperature； so the ocean is a safe and comfortable habitat。 The water in the oceans also keeps the temperature of the earth steady by absorbing and releasing heat。
热容量是一种物质升高一摄氏度所需要的能量。水的热容量相对来说较高。
水能在自身温度不会发生很大变化的情况下吸收和释放许多热量，因此它所创造的环境相当稳定。很多动植物对大范围的温度的剧裂变化都是很敏感的，所以海洋是一个安全而又舒适的栖息地。海洋水还通过吸收和释放热量而使地球的温度保持稳定。
OCEAN MOTION 海洋的运动
Since changes in salinity and temperature affect water’s density； the water in the ocean is always moving。 Dense water sinks and less dense water is pushed to the surface。 This circulation adds energy to the marine ecosystems and moves nutrients around。 Most of the life in the ocean is found in the first two hundred meters of water。 The sun does not reach below this point and few species go any deeper。 But； there is life even on the bottom or floor of the deepest oceans。 The creatures on the ocean floor manage to survive without sunlight and get energy from other sources。
因为海水的盐度和温度影响，海水的密度也会发生变化，因此，海洋里的水经常移动。高密度的水下沉，较低密度的水被推向海面。
这种循环为海洋生态系统增加了能量从而使营养物质四处运动。海洋中的大多数生物一般都生活在水�