Why Is the Water in a Lake Blue
Lake water，as anyone knows who has scooped up some in his hand，is really colourless．The blue colour of a lake is caused by sunlight．When sunlight falls onto the lake，especially where the Water is deep and clear，the blue rays of sunlight are reflected up into our eyes，and the water looks blue．Water in the ocean looks blue for the same reason．
为什么湖水是蓝色的
任何人只要用手舀起一点湖水看一看，就会知道湖水确实是没有颜色的。湖水之所以呈现蓝色是由于阳光照射而引起的。当阳光照入湖中，特别是照到水又深又清澈的地方时，阳光中的蓝光线就反射上来，映入人们的眼帘。于是湖水看上去像是蓝色的。海洋的水呈现蓝色，其道理也是一样。
Why Does a Geyser Erupt
A geyser is caused by heat deep in the earth warming up groundwater in a tubelike crack in the earth’s surface．Deep down at the bottom of the geyser hole，the water is heated well beyond its normal boiling point．As the water grows hotter，the rising steam pushes up the column of water in the geyser hole，until SWOOSH！The geyser erupts in a jet of superheated steam．When water refills the geyser hole and becomes hot enough to boil，the geyser will erupt again．
喷泉为什么会迸发
喷泉是由于地球深处的热量使地球表层中管状裂缝里的地下水变热而引起的。在喷泉孔底层的深处，地下水常常被加热超过正常的沸点。当水变得越来越热时，往上冒的蒸汽就推动喷泉孔里的水往上喷，从而使泉水喷涌而出。喷泉是以超热蒸汽的喷射形式迸发出来的。当水再灌满喷泉孔并变热到足以沸腾时，喷泉将再次迸发。
What Causes Thunder
During a thunderstorm，electrical charges are built up in the clouds．If the charges be come great enough，a lightning occurs．As the lightning bolt jumps across tile sky，it quickly heats the air in its path．The heated air quickly expands and rushes outward just as violently as if there had been an explosion！This causes a great sound wave which we hear as thunder．
什么引起打雷
雷雨时，电荷不断地在云层集结。如果电荷量变得足够强大，就会发生闪电。当闪电横穿天空时，能很快使沿途的空气变热。变热了的空气迅速膨胀，并像发生爆炸那样猛烈地向四周冲击。这样就引起了巨大的声波，这种声波我们听起来就是雷声。
How Can I Locate the North Star
On clear nights it is possible to tell directions by the North Star，just as sailors have done for hundreds of years．One way to locate the North Star is to look for the Big Dipper．The two stars at the front of the dipper’s cup are called the Pointers．An imaginary line drawn through them points to the North Star．（The North Star is the end star in the handle of the Little Dipper．）
怎样找出北极星
在晴朗的夜晚，可以根据北极星来辨别方向，正像几百年来水手们所做的那样。找北极星的一个方法就是找出北斗七星。在北斗星座前的那两颗星叫做指极星。穿过这两颗星划出一条虚线，此线所指的就是北极星（北极星是小北斗星座的最后那颗星）。
Why Is It Cooler in the Mountains
The higher up we go，on a mountain or up in a plane，the less air there is above us．The thinner the air becomes，the cooler it gets，because the air cannot absorb as much heat from the sun’s rays as it is able to hold at lower elevations．We often see snow on high mountain tops during the summer because the temperature is too cold for all the snow to melt．
在山上为什么比较冷
在高山或飞机上，我们离开地面越高，上边的空气就越稀薄。空气越稀薄就显得越冷。因为空气不能从太阳光中吸收像在海拔较低的地方所能吸收的那么多的热量。在夏天，我们常常看到在高山顶上还有积雪，这是因为那里的温度太低，以至于雪无法融化。
What Is Hard Water
“Hard water”is water which has dissolved large amounts of certain minerals．Hard water requires lots of soap to make lather．The minerals also stick to the sides of pipes and boilers and form a crust like scale．Water containing fewer minerals and in which soap will make good suds is called “soft water”．
什么是硬水
“硬水”是含有大量被溶解了的矿物质的水。硬水需要大量的肥皂才能起泡沫。矿物质能粘在水管和锅炉的边壁上，形成了硬壳似的水垢。另一种水含矿物质较少，而且肥皂在其中很容易起泡沫，这种水叫做“软水”。
What Makes the Wind Blow
Wind is moving air．All winds，from gentle breezes to raging hurricanes，are caused mainly by the uneven heating of the earth’s surface by the sun．The land in a warm area heats the air above it．As the air gets warmer，it also gets lighter and rises.As the warm air rises，cooler air from a cooler region pushes in to take its place．This movement of warm and cool air makes a wind．
风是什么引起的
风乃是流动的空气。所有的风，从柔和的微风到狂暴的飓风，主要是由于太阳照射而造成地球表面热的不平衡所引起的。温暖地带的大地能使它上面的空气变热。当空气变热后，它就变得比较轻并且开始上升。当热空气上升时，比较冷的空气就从比较冷的地带涌来，代替热空气的位置。这种热空气和冷空气的流动就形成了风。
Why Does an Ice Cube Float
Water expands when it freezes．Ice takes up about 1/10more room than it did as water．Thus，an ice cube is lighter than an equal volume of water and will float in it．When an ice cube is floating，about 1/10of it is out of water．Because ice decreases about 1/10in size as it melts，the water from the melted ice will take up only as much space as the ice cube took up when it was floating．That’s why the water level in a glass doesn’t rise as the ice cube melts6．
为什么冰块会浮起
当水结冰时，它就会膨胀。冰所占的空间比水多十分之一。因此冰块比同量的水要轻，所以它能在水面浮起。当一块冰块漂浮时，大约有十分之一要露在水面外。由于冰融化时，它大约要减少十分之一的体积，所以冰化成水后仅占据原先冰块漂浮时所占的那么大的空间。这就是为什么当冰块融化时，杯里的水位不再升高。
How Did the Earth Get Its Name
The name“Earth”comes from the old English word“Eorthe”．Before people had the idea of the earth as a planet，our word“Earth”simply meant the ground on which people walked．The word later came to mean the world itself，as well as the ground beneath our feet．
地球是怎样得名的
“Earth”（地球）这个名字是来自古英语的“Eorthe”这个词。当人们不知道地球是个行星时，“Earth”这个词只是表示人们在它上面行走的大地。后来这个词不仅是表示我们脚下的大地，而且渐渐地表示整个世界本身。
What Makes the Rings Around the Moon
