Here are the best options to complete the sentences based on common knowledge about the chicken and egg debate:

1. **Which came first in the world?**
**B. Egg** (This is a common philosophical question suggesting the egg appeared before the chicken.)

2. **How long have people argued for the question which came first, the chicken or the egg?**
**D. For many decades** (This question has been debated for a long time.)

3. **What birds lay eggs?**
**B. Female birds** (Only female birds lay eggs.)

4. **What kinds of egg do people eat much in Canada?**
**C. Chicken egg** (Chicken eggs are the most commonly consumed.)

5. **How heavy is an ostrich egg?**
**B. 1.5 kg** (Ostrich eggs typically weigh around this amount.)

6. **What is inside a normal egg?**
**D. Yolk and white** (A regular egg contains both the yolk and the egg white.)

7. **How does the white change when it is boiled?**
**A. It turns white.** (The egg white solidifies and turns white when boiled.)

8. **What is correct?**
**C. Eggs are good for health.** (Generally accepted in nutrition as beneficial when eaten in moderation.)

Feel free to ask if you have more questions!