You stare at waterfall for a minute or two, then shift your gaze
to its surrounding. What you now see appears to drift upward. You __1__
are board a train in a busy station when suddenly another train next __2__
to your starts moving forward. __3__
For a fraction of a second you feel that your train has lurched
backward. These optical illusions occur because the brain is
constantly matching its model of reality to signals from the body’s
sensors and interpret what must be happening – that your train __4__
might have moved, not the other; that downward motion is now __5__
normal, so a change from it must be perceived as upward motion.
The sensors that make this magic are two kinds. __6__
Each eye contains about 120 million rods, which provide some-
what blurry black and white vision. These are the windows of night
vision; once adapted to the dark, they can detect a candle burnt __7__
ten miles away. Colorful vision in each eye comes from six to seven __8__
million structures called cones. Under ideal conditions, every cone
can “see” the entire rainbow spectrum of visible colors, but one
type of cone is most sensitive to red, another to green, the third to __9__
blue.
By monitoring how many wavelength of light affects the different
cones, a connected ganglion cell can determine its “color” and relay
that data brainwork. Rods and cones send their messages pulsing an __10__
average 20 to 25 times per second along the optic nerve.

答案及解析:
1.surrounding－surroundings
surroundings作为名词总是以复数形式出现，surrounding是形容词。

2.board－aboard；^board－on
be abroad a train ( a ship, a plane…)意思是“在火车（船、飞机）上”。board 是名词，可以说be on board （这个改错之前也出现过，经常出现的大家可都要记住啦）

3.you－yours
物主限定词your不能作介词的宾语，应该用物主代词yours。

4.interpret－interpreting
Interpret 通过and 和matching并列，所以也应该是进行体形式。

5.might－must
根据上下文，这里必须用表达非常肯定的语气must，而不是不肯定的“might”，而且，后面的not the other也强调了非此即彼的肯定性。

6.are^－of
加上介词of作主语补足语表示对主语的某一种性质的描述。

7.burnt－burning
如果用过去分词burnt修饰candle，那么是说“十英里之外燃尽的蜡烛”，那是不可能用肉眼看到的，所以应该改成burning，表示“在燃烧的蜡烛”。

8.Colorful－Color
Colorful是指所修饰的事物本身具有明亮的或者不同的颜色，而color作定语是指修饰的事物使别的事物的各种颜色能够展现出来，而不是仅仅看到黑白两色，比如：color television，color photo，color picture等。

9.the－a
the third 表示顺序排列，和the first， the second 对应，“a third”表示数量上的增加，和one，another相对应。

10. that－those
data这个词是datum的复数形式，所以应该用those修饰