单选题 Sometimes something looks different from another thing but it is usually the same. Sometimes something looks the same s another thing but it is really different.
Sometimes we can not believe our eyes. Here is an example. If we are standing in front of an entrance of a tunnel, we can see the other end where we go out. We feel the entrance much bigger than the other end. If we go through the tunnel, we find that the ends are the same size. One is not bigger than the other. They are the same.
Now let's turn around and look through the tunnel from the other end. Now we find that the end near us looks bigger. The other end looks smaller. But we know that they are the same size.
Things that are near us seem big. Things that are far away from us seem small. We know that one lamp-post in the streets is just like another. They are all equally tall. But if an artist draws a picture of a street he will not make the lamp-posts all the same size. He will make the first one big, and the second one a bit smaller. Then the next one a little smaller. The ones that are the farthest away are the smallest. When things move away they look smaller. When things come nearer they look bigger.