A、Until he eats it. B、At least thirty minutes. C、All day. D、No more than thirty minutes. D食物应该给狗留多长时间，本文第三段首先回答了，在任何情况下都不能超过30分钟

When you have a dog it is necessary to care for it very carefully. In return you will be loved by your dog as a kind of monarch who is loved by his people.
    Proper feeding is also important to your dog’s health. Heavy aluminum feeding pans are best since they cannot chip or break. A dog should be fed in the same place and on a regular schedule. During feeding time it should be quiet. If your dog refuses to eat, don’t force him. Remove his food and don’t feed him again until his next regular feeding.
    (26) Food should never be left before a dog for more than thirty minutes under any circumstances. If he does eat over a long period of time, your dog should be taken to a veterinarian. Another important thing is to keep fresh water available to the dog during hot weather.
    One important thing that many dog owners forget is exercise for their dogs. Vigorous exercise helps build strength and keeps the dog healthy. Without it the dog’s development is impeded. A regular walk at a fixed time of the day is enough to help a small dog live a healthier and happier life. (27) Large dogs, though, require a nm in an open field.
    There are other things that are also important for a dog’s health-things like bathing, care of the teeth and nails, keeping them away from insects as much as possible. (28) But if you observe the three main points covered above, your dog will give you a great amount of pleasure.