Man's best friend dog is colorblind, but (fortunate), his survival does not depend upon the ability to see colors. His keen (灵敏的) sense of smell makes up for inability to see colors, and (enable) him to differentiate between things.
Extensive scientific testing on dogs supports the conclusion that they live in colorless world. The testing done primarily focused the dogs' responses to colors for food. Dogs could not tell the (different) between one color, a signal for food, and other colors that were not for food. Similar tests (conduct) on cats produced similar results, which led scientists to conclude that they, too, are colorblind and live in a gray world.
The inability of most animals to see colors is quite simple (understand). Many colorblind animals have dark coats, hunt for food in the dark of night or graze (吃草) in the dim twilight (黄昏的)hours. Their other senses have developed to the point the lack of color vision in no way weakens them. For them, life in a colorless world is neither a handicap, a threat to their survival.
is concluded that other than man the only animals with color vision are monkeys and apes. They can be trained to open a colored door, behind which is food.
