拟建一容积为18m3长方体无盖水池，已知侧面单位造价为底面造价的，如何设计尺寸，才能使总造价最省？

C

Life in the Clear

Transparent animals let light pass through their bodies the same way light passes through a window. These animals typically live between the surface of the ocean and a depth of about 3，300 feet—as far as most light can reach. Most of them are extremely delicate and can be damaged by a simple touch. Sonke Johnsen， a scientist in biology， says， “These animals live through their life alone. They never touch anything unless they’re eating it， or unless something is eating them.”

And they are as clear as glass. How does an animal become see-through？ It’s trickier than you might think.

The objects around you are visible because they interact with light. Light typically travels in a straight line. But some materials slow and scatter（散射） light， bouncing it away from its original path. Others absorb light， stopping it dead in its tracks. Both scattering and absorption make an object look different from other objects around it， so you can see it easily.

But a transparent object doesn’t absorb or scatter light， at least not very much， Light can pass through it without bending or stopping. That means a transparent object doesn’t look very different from the surrounding air or water. You don’t see it ————you see the things behind it.

To become transparent， an animal needs to keep its body from absorbing or scattering light. Living materials can stop light because they contain pigments（色素） that absorb specific colors of light. But a transparent animal doesn’t have pigments， so its tissues won’t absorb light. According to Johnsen， avoiding absorption is actually easy. The real challenge is preventing light from scattering.

Animals are built of many different materials————skin， fat， and more————and light moves through each at a different speed. Every time light moves into a material with a new speed， it bends and scatters. Transparent animals use different tricks to fight scattering. Some animals are simply very small or extremely flat. Without much tissue to scatter light， it is easier to be see—through. Others build a large， clear mass of non-living jelly-lie（果冻状的）material and spread themselves over it .

Larger transparent animals have the biggest challenge， because they have to make all the different tissues in their bodies slow down light exactly as much as water does. They need to look uniform. But how they’re doing it is still unknown. One thing is clear for these larger animals， staying transparent is an active process.

63. According to Paragraph 1， transparent animals_______.

A.stay in groups

B.can be easily damaged

C.appear only in deep ocean

D.are beautiful creatures

LEDs are different from light bulbs in that______.

A．LEDs are made up to tiny pieces of rock

B．LEDs can send out light of different colors

C．LEDs belong to incandescent lights

D．LEDs look like crystals

The best way both for reading and for writing is to________．

A.sit facing the light

B.1et the light shine from your back

C.sit with your right side towards the light

D.have the light come from your left

A．from which

B．to which

C．at which

D．in which

When drinking the green tea, you ______.

A．have to add some milk or sugar to its light flavor

B．perhaps don't like its astringent flavor

C．may have different choices according to your taste

D．can't tell it from the other kind of teas

______ in this way, the two notions are the same thing seen from different perspectives.

A．To look at

B．Looking at

C．Looked at

D．To be looked at

______ in this way, the two notions are the same thing seen from different perspectives.

A．To look at

B．Looking at

C．Looked at

D．To be looked at

How is television different from radio？

A．Sound is changed into electromagnetic waves.

B．Light is changed into electromagnetic waves.

C．Both sound and light are changed into electromagnetic waves.

D．Either sound or light is changed into electromagnetic waves.