Question

Secrets of the Rainbow

The storm is over: the sun is shining. But when you go outside, the rain is still falling, and you see a breathtaking sight in the sky: a shimmering arch of red, orange, yellow, green, blue and purple light. No pot of gold sits at that rainbow’s end.1. Rainbows are rare because they need two things that don’t often go together: sunlight and rain.2.But it contains all the colors of the rainbow. A rainbow appears when raindrops split these colors apart, letting us see them.

In empty space, all these colors travel equally fast: 671 million miles an hour. But when sunlight passes through water, it slows down. 3. These differences in speed make a rainbow. Red light goes fastest. Orange is almost as fast. Yellow is a little slower, and green is a little slower than that. Blue is slower still, and purple light is the slowest.

As light enters water, it bends, or refracts (折射). The amount of refraction depends on how fast the light travels through water. So once sunlight enters a raindrop, the different colors split apart and travel separate paths. 4. They exit the front of the raindrop, bending again as they go from water to air. So they are still on separate paths, with the different colors next to one another, and you see a rainbow when you look at the falling raindrops.

After you find a rainbow, look for a second rainbow outside the main one. It’s called a secondary rainbow and is usually fainter, so it’s harder to see. 5. The main rainbow has red on top and purple on bottom. The secondary rainbow has red on bottom and purple on top.

A.Sunlight usually looks pale.

B.Its colors are in the opposite order.

C.Instead, a rainbow is its own reward.

D.There’s more to a rainbow than we can see.

E.Some colors go through water faster than others.

F.Then the colors reflect off the back of the raindrop.

G.A rainbow only needs the right mix of sunlight and rain.

Answer

1.C

2.A

3.E

4.F

5.B

【解析】

这是一篇说明文。文章主要介绍了彩虹是如何产生的，以及主彩虹和次级彩虹之间的区别。

1.

根据上文No pot of gold sits at that rainbow’s end.可知彩虹的尽头没有一罐金子。以及后文Rainbows are rare because they need two things that don’t often go together: sunlight and rain.可知彩虹之所以罕见，是因为它们需要两种不常同时出现的东西：阳光和雨水。由此可知，彩虹因为很罕见，所以对人们来说能看到彩虹本身就是一种奖赏，故C选项“相反，彩虹本身就是奖赏”符合语境，故选C。

2.

根据后文But it contains all the colors of the rainbow. A rainbow appears when raindrops split these colors apart, letting us see them.可知但是它包含了彩虹的所有颜色。当雨滴把这些颜色分开，让我们看到它们时，彩虹就出现了。由此可知，本句是在说明阳光的特点，阳光通常看起来很白，但是它包含了彩虹的所有颜色。后文it即指代A选项中的sunlight。故A选项“阳光通常看起来很白”符合语境，故选A。

3.

根据上文In empty space, all these colors travel equally fast: 671 million miles an hour. But when sunlight passes through water, it slows down.可知在空旷的空间里，所有这些颜色的传播速度都一样快：每小时6.71亿英里。但是当阳光穿过水时，它的速度就会减慢。以及后文These differences in speed make a rainbow.可知这些速度上的差异造就了彩虹。由此可知，颜色在水中穿过的速度是有差异的，有的快有的慢，所以这些速度上的差异造就了彩虹。故E选项“有些颜色在水中穿过的速度比其他颜色快”符合语境，故选E。

4.

根据上文So once sunlight enters a raindrop, the different colors split apart and travel separate paths.可知因此，一旦阳光进入雨滴，不同的颜色就会分开，以不同的路径传播。由此可知，上文提到了阳光穿过雨滴，那么本句应当是说明穿过雨滴之后，颜色会在雨滴的背面反射。故F选项“然后颜色在雨滴的背面反射”符合语境，故选F。

5.

根据后文The main rainbow has red on top and purple on bottom. The secondary rainbow has red on bottom and purple on top.可知主彩虹红色在最上面，紫色在最后。次级彩虹红色在最后，紫色在最上面。由此可知，主彩虹和次级彩虹的颜色顺序是相反的。故B选项“它的颜色顺序相反”符合语境，故选B。