Every so often, birds, just like humans, do what it takes to feel really, really good. The bird version is to sit on an anthill  so that hundreds of ants climb all over their bodies, or even better, some birds pick up mouthfuls of pressed ants and rub themselves all over. Afterwards, the birds either eat the ants or set them free.     Scientists call this "anting." It's a common bird practice, and is especially done by the smarter birds. Ravens do it. Magpies do it. However, birds aren't the only animals that use anting --- squirrels, cats, and hedgehogs have all been observed doing the same sort of thing!     Why birds "ant" is something of a mystery, but one thought is acceptable. Ants have defensive secretions , chemical weapons they use to fight off other insects and bacteria. So pressed ants help the birds drive the insects away. Similarly, if you cover your body with them, you can move through the forest without worrying about being bitten by insects. Plus, ants are cheap. They are around.     However, we have a better explanation. Birds "ant" a lot in spring and summer. For many birds, that's the season for birds to change feathers. So maybe ant secretions are like bath oil; they comfort the skin during feather replacement. A British scientist once declared "the purpose of anting the stimulation  and comfort of the body," and that the general effect "is similar to that gained by man from the use of outside stimulants, and perhaps also smoking."     And like cigarettes, anting can become a habit. Another study compares anting to "the human habits of smoking and drug taking," and says, "it is enjoyed for the feeling of excitement it results in. So once experienced, it is difficult to stop." That's why you often see mother birds shouting at their babies who come near their first anthill. "Stay away from there, child... Don't touch those ants!" they cry. I don't speak Raven. Or Magpie. But I have been a parent. So some things I know. The practice of anting   _  .
is unique to birds is a rare phenomenon makes birds feel comfortable provides a main food source for birds
Question: Every so often, birds, just like humans, do what it takes to feel really, really good. The bird version is to sit on an anthill  so that hundreds of ants climb all over their bodies, or even better, some birds pick up mouthfuls of pressed ants and rub themselves all over. Afterwards, the birds either eat the ants or set them free.     Scientists call this "anting." It's a common bird practice, and is especially done by the smarter birds. Ravens do it. Magpies do it. However, birds aren't the only animals that use anting --- squirrels, cats, and hedgehogs have all been observed doing the same sort of thing!     Why birds "ant" is something of a mystery, but one thought is acceptable. Ants have defensive secretions , chemical weapons they use to fight off other insects and bacteria. So pressed ants help the birds drive the insects away. Similarly, if you cover your body with them, you can move through the forest without worrying about being bitten by insects. Plus, ants are cheap. They are around.     However, we have a better explanation. Birds "ant" a lot in spring and summer. For many birds, that's the season for birds to change feathers. So maybe ant secretions are like bath oil; they comfort the skin during feather replacement. A British scientist once declared "the purpose of anting the stimulation  and comfort of the body," and that the general effect "is similar to that gained by man from the use of outside stimulants, and perhaps also smoking."     And like cigarettes, anting can become a habit. Another study compares anting to "the human habits of smoking and drug taking," and says, "it is enjoyed for the feeling of excitement it results in. So once experienced, it is difficult to stop." That's why you often see mother birds shouting at their babies who come near their first anthill. "Stay away from there, child... Don't touch those ants!" they cry. I don't speak Raven. Or Magpie. But I have been a parent. So some things I know. The practice of anting   _  .
A. is unique to birds
B. is a rare phenomenon
C. makes birds feel comfortable
D. provides a main food source for birds
Answer: