15．When a big boat，like a cruise ship，goes through the ocean，it often creates waves．This happens when the large engines on the back of the cruise ship cause the water on the ocean's surface move up and down violently．These waves move out from the boat in both directions．If you are captaining a smaller boat，you'd better steer clear of a ship's wake，so that your boat is not surfing on the waves，causing it to overturn．
A wave is a pattern of motion．When you look at a wave，it may appear as simply water moving across the surface of the ocean．In fact，this is false．The water is actually not moving in the same direction as the wave．While the wave itself-the pattern of motion-is moving across the surface of the ocean，the water is actually moving in a circular motion，which brings the water molecules back to their original position．The water merely gives the appearance of moving forward．
If this is confusing，think of the kind of wave you do at a baseball stadium．Viewed from a distance，the wave is clearly moving across the stadium．But the thing that makes up the wave-the people-are not moving across the stadium，they're just moving up and down in their seats．This is just like the water in an ocean wave．A lot of water is moving up and down，which gives water the appearance of moving along with the wave．
Surfers pay a lot of attention to waves．If you're not in an area where the waves are suitable for surfing，then you can't surf．Usually，surfers gather in areas known for big waves-waves that rise high off the ocean's surface．If the wave is bigger，then the surfer is often able to surf for longer distances and perform more tricks．The height of a wave is known as its amplitude．If you could make a wave freeze，then you could measure the wave's amplitude by running a tape measure from the ocean's surface to the very peak of the wave．
All waves can be measured using amplitude and wavelength．While the waves created by a boat have very small amplitude-sometimes as small as a few centimeters-the wavelength can be very short，as lots of waves are being generated．By contrast，a tsunami has very high amplitude，sometimes more than 100 feet，but a relatively long wavelength，as it's a high wave．
Waves generated in the same way can have great differences in amplitude and wavelength．For example，think back to the cruise ship．While each ship creates waves caused by the movement of the boat，the properties of each of the waves may be very different．For example，a larger cruise ship，with powerful engines，may create a wave that has high amplitude and a short wavelength．However，if the ship's engines slow down，they may then start creating less powerful waves at a slower rate．This would cause the waves'amplitude to decrease，but its wavelength to increase．
61．What does the phrase"steer clear of a cruise ship's wake"in the 1st paragraph mean？D
A．Keeping awake while steering a ship．
B．Getting a clear view of what is ahead．
C．Following the cruise ship very closely．
D．Keeping away from the cruise ship．
62．The author gives an example of wave people do in the stadium in order toC．
A．illustrate how excited people are in a basketball stadium
B．clear the confusion over measuring the wave's amplitude
C．explain why the water appears to move along the waves
D．demonstrate how to make waves in a basketball stadium
63．The last paragraph gives us the impression thatC．
A．the wave's amplitude may vary，but its wavelength remain the same
B．the amplitude of a wave depends on the direction the water moves forward
C．the more powerful the ships'engines are，the higher the waves they generate
D．measuring the amplitude and wavelength of waves is not quite easy
64．What is this passage mainly about？D
A．What makes the sea water move forwards．
B．How to steer a cruise ship in the rough sea．
C．Why people create waves in the stadium．
D．How waves are created and measured．
分析 本文是一篇科教类阅读，属于说明文，当一艘像游轮这样的大船穿过海洋时，经常会产生波浪．当游轮背面的大型引擎使海洋表面的水猛烈地上下移动时，就会发生这种情况．本文以此展开，主要讲述了波浪是如何产生和度量的．
解答 61．D．词义猜测题．根据上下文内容可知，If you are captaining a smaller boat，you'd better steer clear of a ship's wake，so that your boat is not surfing on the waves，causing it to overturn．句意为如果你拥有一条较小的船，你最好远离游轮，让你的船不会在海浪上冲浪，导致它翻船．故 steer clear of a ship's wake意为远离游轮．故选D．
62．C．细节理解题．根据A lot of water is moving up and down，which gives water the appearance of moving along with the wave．可知，作者举例是为了解释为什么水似乎沿着海浪移动．故选C．
63．C．推理判断题．根据For example，a larger cruise ship，with powerful engines，may create a wave that has high amplitude and a short wavelength．However，if the ship's engines slow down，they may then start creating less powerful waves at a slower rate．This would cause the waves'amplitude to decrease，but its wavelength to increase．可知，本段告诉我们了船舶发动机越强大，它们产生的波浪越高．故选C．
64．D．主旨大意题．阅读全文，根据全文内容可知，本文主要讲述了波浪是如何产生和度量的．故选D．
点评 本文是一篇科教类阅读，题目涉及多道主旨大意题，细节理解题，推理判断题．做题时学生应仔细阅读原文，把握文章主要内容，联系文章上下文内容并结合所给选项含义，从中选出正确答案，一定要做到有理有据，切忌胡乱猜测．
