Here are the correct answers based on the passage:

1. **What do the doctors advise us to do every morning?**
**C. Drink a glass of water**

2. **According to the passage, what can the intestines do after we drink water?**
**A. Prepare for digestion smoothly**

3. **How much water do the scientists suggest that people should drink a day?**
**1,600 milliliters** (Note: This specific answer isn't listed in the options, but it's the information given in the passage.)