根据短文内容，从短文后的七个选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。 Why Cats Scratch Things It has long been assumed that when cats scratch objects with their front paws (爪子) that they are sharpening their paws. 1_____ Research on cat behavior suggests that the major reason for this behavior is communication. By scratching up the bark of a tree (or the leg of your favorite chair) the cat is letting other cats or people know where she is and what she is up to. Cats tend to pick a small number of noticeable objects in their environments to scratch such as trees, fence posts repeatedly. 2_____ The scratched suce leaves a highly visible mark that can be easily seen by other cats. In addition, cats have special glands (腺) in their paves so that when they make scratching movements they leave scent (气味) that the cats can smell. The fact that cats leave scent marks by scratching movements may be the reason that cats will continue to try to scratch objects even after they have been declawed. 3_____ We don't know exactly what cats are communicating with their scratching. Both males and females do it. It is done inside and outside the home and even by cats living with no other cats around. 4_____ Cats don't scratch up your furniture to bother you or just to be destructive, but for specific reasons, one of which is communicating. Cats also scratch to extend their bodies, during play, and possibly as a greeting or to relieve dissatisfaction when pred from doing other things they want to do. 5_____ It is easier to pr problem scratching rather than trying to change your cat's preference for the arm of your sofa after it has become a built up habit. Thus, the goal is to establish acceptable scratching habits by getting your cat to prefer a scratching post rather than the arm of your sofa. A. It turns out that this is only a secondary reason. B. This is why the tree next door looks so scratched up. C. Cats use other parts of their bodies to communicate as well. D. Small pieces of bark have accumulated on the ground underneath. E. Scratching can result in considerable damage, owner dissatisfaction. F. Declawed cats may still be leaving scent marks on objects they scratch. G. It could be a defensive warning or just a marker that announces its existence.