Here are the correct answers for the questions in the provided text:

**Mark A, B, C, or D to indicate the word that differs from the other three in the position of primary stress:**
6. A (decide)
7. B (hygiene)
8. D (listen)

**Choose the option (A, B, C or D) that best completes each of the following sentences:**
8. **D (passed down)** – This traditional company has been passed down from parents to children over many generations.
9. **A (higher)** – Mr. Buong thinks the bigger the city is, the cost of living is higher.
10. **B (picks)** – Alex rarely uses the bus, so his mother often picks him up at school.
11. **C (turns)** – Ha Noi is like a concrete jungle with so many people in it. It's an bustling city.
12. **D (peaceful)** – The more the city gets, the more congested the streets are.
13. **C (more crowded)** – I am often carsick because of the smell of car exhaust, so I like getting around by taxi.
14. **B (private car)** – It is often more peaceful to live in the suburb than in the city.
15. **D (expensive)** – My neighborhood is very noisy and dusty because there is a supermarket there now.
16. **B (supermarket)** – Many young people in the city spend the whole day playing games in an entertainment center.
17. **C (value)** – I think they may be big companies in urban areas as they make noisier.
18. **B (will build)** – All the students in this city will build the museum carefully before going to school.
19. **B (might)** – The museum in this city is small; it has many unique pictures.
20. **D (Because)** – As the museum in this city is small, it has many unique pictures.

Feel free to ask if you need further assistance!