Sure! Here are the sentences created from the cues provided, as well as questions for the underlined phrases about the Katu ethnic group in Vietnam.

### Sentences from Cues:

1. Which ethnic group has the second largest population in Vietnam?
2. The Sáp dance is a typical dance of the Muong people in the north.
3. Most ethnic minorities in Vietnam live in mountainous areas.
4. The Thai ethnic minority is well known for beautifully woven garments.
5. The New Year celebration of the Lao ethnic group is held in lunar April.
6. The Katu people account for approximately 1.8% of Vietnam's population.
7. The Tay people live in fertile plains and they cultivate rice and keep cattle and poultry.
8. How long have the Ede lived in the high plateau region of central Vietnam?

### Questions for Underlined Phrases about the Katu Ethnic Group:

1. How many Katu people are there?
2. Where do they live mainly?
3. How would you describe the Katu in terms of personality?
4. What are the traditional dances of the Katu?
5. When do they hold the rice spirit feast?
6. What are the Katu known for in relation to their annual buffalo-sacrifice ceremony?
7. What custom related to tattoos have Katu women traditionally practiced?
8. How does the Hmong group compare to other ethnic minorities in Vietnam?
9. How far is it from Hanoi to Ha Giang where the Lolo people live?
10. Which ethnic group has the biggest number of population in our country?

Feel free to let me know if you need further assistance!