Sure! Here are the completed sentences:

1. My uncle has **a** coffee plantation in Kon Turn.
2. How **many** ethnic groups live on the Hoang Lien Son mountain range?
3. There are only **a few** waterwheels left in my village.
4. You should add **a little** more water to your noodles. It's a bit dry.
5. How **much** information about the Van Kieu have you collected?
6. In our area, it has not **much** land for growing crops.
7. We haven't got **much** petrol. We need to stop and get some.
8. You travel a lot. Have you been to **many** countries?
9. There was **a little** food in the fridge. It was nearly empty.
10. It costs **much** money to give your children a good education.
11. There aren't **many** things to do in this village.
12. How **much** sugar do you take in your tea?
13. Dad, I need **a little** money for school.
14. There are **many** things that you can do to improve your writing.
15. My grandfather taught me to sing **a few** folk songs.