魔法英语课文译注(高二·下)-第4章
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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下二百米处。
在这个深度之下，太阳就照不到了，所以很少有生物能到海洋的更深处。但是，即使在最深的大洋底部也有生命存在。生活在大洋底部的生物必须在没有阳光的情况下生存，并且能利用其他能源。
重点、难点、考点及疑点解释
1。What is it that makes the ocean such a great place to live？ 什么使得海洋成为这么好的生活环境？
此句为强调句式的疑问句。强调的部分为what。若把此句变成陈述句则为 It is what that makes the ocean such a great place to live。
2。The chemical structure of water makes it an excellent medium for life。
水的化学结构使得成为生命存在的奇妙的载体。
（1） medium n。表示“媒介物；藉以生存之物或环境；介质”之意。
Commercial television is a medium for advertising。商业电视是一种广告媒介。
A fish in water is in its natural medium。 鱼在水中，自得其所。
medium也可作形容词，表示“中等的；中庸的；普通的”之意。
medium wave中波
He is of medium height。他是中等身材。
（2） make it ＋名词、形容词结构表示“使得……成为；使得……怎样”之意。
His hard working made him a success。他的努力使得他成为成功人士。
Chemical structure of water also makes it different from almost everything else on earth。
水分子的这种结构使得它成为地球上独一无二的东西。
3。The nutrients in whatever falls into the ocean will quickly become available to other living creatures。 流入海洋里的任何营养物都会马上被其他的生物所利用。
此处的whatever＝ anything that。in whatever falls into the ocean为定语从句，修饰the nutrients。
available为形容词，表示“可得到的；可利用的”之意。
He is not available for the job。他不适宜做这个工作。
These tickets are available for one month。这些票有效期一个月。
4。Density is the relationship between mass and volume and is measured in kilos per cubic meter （kg/m3）。密度是质量和体积之间的关系，通常用每千克/立方米为测量标准。
（1） relationship名词，表示“关系，联系”之意。
Do you know her relationship to that girl？
你知道她和那个女孩有什么亲戚关系吗？
The teacher has a very good relationship with her students。 这位老师和学生们关系很好。
（2） mass名词，表示“大团、块，（物）质量，大量”等的意思。
Before the rain； the sky has a mass of clouds。 下雨前，天空有一团云。
the law of conservation of mass质量守恒定律
（3） sth。 be measured in kilo为“某物以公斤为测量单位”，其中的介词in为“用”的意思。
Heat is measured in calorie。 热量是用卡来计算的。
有时表示用by来表示“用时间，长度，重量，数目”等。
sell the cloth by the yard按码来卖布
sell the coal by the ton。按吨来卖煤
pay the workers by the day按天给工人报酬
get charged by weight / time 以重量/时间来收取费用
5。If a substance has a higher density； say 5；000kg/m3； it will not float in water。 如果某种物质的密度较高，比如说为5000kg/m3，它就会浮在水上。
此句中的动词say不再是“说”的意思，而是“比如说；姑且说；假定说；大约”之意，常用于虚拟语气或祈使句中。
The number left was not great； say； only ten。余下的数目不大，姑且说，只有十个罢。
Say your plan fails； then what do we do？假定你的计划失败了，那么我们怎么办呢？
6。Marine animals and plants take advantage of the density of water。海生动植物利用了海水的密度。
advantage可数名词，意为“优势；长处”，其反义词为disadvantage（缺点，不利）。
Mary speaks good English； but she has an advantage because her mother is English。
玛丽英语说得好，因为她有一个有利条件，她妈妈是英国人。
Many women think this is an advantage for men。许多妇女认为这是男人的优越之处。
His bad health is a great disadvantage for him to get a good paid job。
他体弱多病对他求得一个薪水很高的工作很不利。
take advantage of sth。 为固定短语，表示“（乘机）利用，欺骗”之意。
He always takes advantage of mistakes made by his competitors。他常常会利用竞争对手的错误。
7。Water can absorb and release a lot of heat without big changes in its temperature； thus creating a stable environment。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。
（1） absorb为动词，表“吸收（液体）；吸取（知识）；使专心”之意。短语be absorbed in sth。为“专著于……”之意。
This job absorbs all of my time。这件工作占有了我的全部时间。
The writer was absorbed in his writing that he forgot to flick the ashes from his cigar。
作家全神贯注地进行写作；以致于忘了弹去雪茄烟的烟灰。
（2） thus creating a stable environment为分词短语表结果。stable为形容词，其近义词steady在下面句子中也出现了。注意他们各有侧重：
stable表示“稳定的，坚固的；意志坚定的，不动摇的；可靠的”，多用来修饰一些抽象的概念。
stable peace稳固的和平stable opinions坚定的意见
a man of stable character性格坚定的
Markets are flourishing and prices are stable。市场繁荣，物价稳定。
steady多用来修饰物体的平衡性，动作的稳健，速度的稳定等客观事物。
to make a table steady使桌子牢靠
not very steady on one’s leg步履不太稳定
a steady wind无变化的风
有时两者也可换用：a steady /stable man可靠的人
8。Most animals and plants are sensitive to large or sudden changes in temperature； so the ocean is a safe and a comfortable habitat。很多动植物对周围气温大范围的温度的剧变都是很敏感的，所以海洋是一个安全而且舒适的栖息地。
sensitive形容词，表示“敏感的；感觉敏锐的；易受伤害的”。常与to连用表示“对……敏感”之意。
She is sensitive to what people think of her。她对人们是怎么看待她的很敏感。
The old man is highly sensitive to any unusual sound in the machine
那位老人对机器中任何不正常的声音十分敏感。
9。This circulation adds energy to the marine ecosystems and moves nutrients around。
这种循环为海洋生态系统增加能量从而促进营养物质四处移动。
ecosystem为合成词，由eco＋system构成。eco作前缀，表示“环境、生态、生态学的”之义，system为名词表示“系统”。
UNIT 13 The water planetNATURE'S NURSERY： ESTUARIES 自然之母——河口
If the ocean is the source of life on earth； then the estuary is our planets nursery。 An estuary
is the body of water where a river meets the ocean。 Salt water from the ocean and fresh water from
the river mix together in an estuary。 This mixing of fresh and salt water creates a unique environment filled with life of all kind—a transition zone between the land and sea。 Estuaries are the homes of thousands of animals and plants。 Many cities and towns are built around estuaries；and seventyfive percent of fish are caught in estuaries。
Estuaries are great places for natures young ones。 Here； animals can enjoy all the benefits of the oceans without having to face many of its dangers。 Tides provide energy for the ecosystems； but estuaries are protected from waves and storms by islands； mud； or sand。 Nutrients arrive in estuaries from both the land and the ocean。 The diversity of life in estuaries is incredible—birds； fish； marine mammals； shellfish and other species all come here to live； feed and reproduce。
Estuaries are also important because they absorb nutrients and pollutants from water coming from inland sources； thus cleaning our water。 Unfortunately； this function also makes estuaries very sensitive to environmental pollution。 Since estuaries protect animals and plants from storms and floods and prevent erosion； protecting them is very important。
Finally； estuaries provide both recreation and education for human beings。 Most of us enjoy fishing； swimming and having fun on the beach； and scientists and students have endless opportunities to study a variety of life in the habitat。 Estuaries also contribute to the economy through tourism and fishing。
如果说海洋是地球的生命之源，那么，河口就是我们这个星球之母了。河口是河流和海洋会合的水体。来自海洋的咸水和河流的淡水在河口混合。盐水和淡水混合创造出了一个独特的环境，其中充满了各种生物——这是陆地和海洋的过渡区。河口是成千上万的动植物的家园。许多城市和城镇就建在河口旁边，大约百分之七十五的鱼类都在河口地区捕获的。
河口是许多新出生动物的最好的去处。在这里，动物们可以享受到海洋的所有益处而不必面对�
