A、3. B、4. C、2. D、1. A文中谈到狗的照料时，首先说到了环境的重要性，然后就是食物的干净程度，再次就谈到了锻炼的必要性，这三点就可以保证一个狗的健康了(if you observe the three main points covered

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.