Here are the best answers for each question in the exercise:

1. **A** - Five-coloured sticky rice is **an** important traditional dish.
2. **B** - Thai have **population** of about 1,500,000 people.
3. **A** - Thai women wear short blouses, long skirts, scarves and ornaments.
4. **C** - Which group has the **smallest** population?
5. **A** - There was **an** exhibition of Ethnic Minorities Opens on April 18th at Ly Thai To Flower Garden.
6. **C** - I have **a** shawl. Shawl is unique and strong.
7. **A** - We can find terraced fields in **the** northern mountainous regions.
8. **A** - Look! Flowers my mother bought from **the** market yesterday are blooming.
9. **C** - Is Lien **an** assistant?
10. **B** - My mother does **not** shop in my family.
11. **A** - How many people were there at the family **reunion** last weekend?
12. **D** - We should **raise** children’s awareness of our customs and traditions.
13. **A** - Joe broke with **tradition** when he went to an art college.
14. **C** - We **celebrate** the Spring Festival on the 15th of January in the lunar calendar.
15. **D** - Tourists usually wear shorts and tank tops when attending the worshipping ceremony.
16. **C** - Festivals are important because they keep some village traditions **alive**.
17. **A** - It’s the **habit** in that country for women to get married in white.
18. **C** - Many young people don’t **obey** the tradition of living with their parents when they are eighteen.

Feel free to ask if you need further assistance!