听下面一段材料，回答第1-4题。 1. What is the most important part of dog-care? A. Proper feeding. B. Active exercise. C. Clean. 2. How long should food be left before a dog? A. Not more than twenty minutes. B. Not more than thirty minutes. C. Not more than an hour. 3. Why does a pet dog need active exercise? A. To build its strength B. To help it sleep well. C. To keep it lively. 4. What kind of dog needs to run in an open field? A. An old one. B. A small one. C. A big one.