阅读理解 When you watch 3D movies or TV, you have to wear a special pair of glasses. The 3D glasses make the images from the screen look like they are there in the room with you.
Three-dimensional, or 3D, means having three dimensions（维度）: width, height and depth. 3D technology（技术） is based on the way the human brain（大脑） and eyes work. Because the pupils of a person's eyes are about 6.5era apart（分开）, when we look at something, each eye sees,it from a different angle（角度）. Our eyes send the two images to our brain, and the brain puts them together. The small difference between the image from the right eye and the image from the left eye allows us to see depth.
When we view pictures and television in two dimensions, each eye gets the same information. That is because the image has no real depth, and there is only one of viewing it. So the goal of 3D technology is to get a different image into each of the viewer. It uses two film projectors. One projects a left eye image and the other projects a right image. The 3D glasses allow us to see a different image in each eye.
While watching 3D films, we feel that we are in the same environment as the things we're watching. However, it also has its disadvantages. The 3D glasseswork by controlling the amount of light that reaches the eyes. It makes the screen look darker. What's more, people with eye problems may get headaches if they spend too much time watching 3D movies，because their brains need to work harder to "read" the images.
