Here are the answers based on the passage:

1. **Which ethnic group is mentioned in the passage?**
- **B. The Dao**

2. **How is each Dao group easily identified?**
- **A. by their costumes**

3. **Which of the following is TRUE according to the passage?**
- **C. The Dao ethnic group has a total population of nearly 1.5 million people.**

4. **Why are the Dao Quan Cat called Son Dâu?**
- **A. Because the women shave off their hair, paint their heads, and cover their heads with traditional headscarves.**

If you have any other questions or need further assistance, feel free to ask!