Here are the answers based on standard English usage and context:

**I. Choose the correct answer:**

1. **a** - The
2. **c** - which
3. **b** - family gathering
4. **d** - form
5. **a** - a
6. **c** - should
7. **b** - but
8. **a** - a
9. **c** - could
10. **c** - because

**IV. Choose the underlined word or phrase:**

1. **C** - the fireworks festival
2. **B** - enter
3. **C** - the traditional Vietnamese wedding
4. **C** - important
5. **B** - much
6. **C** - a sign of respectful
7. **B** - A**

Feel free to double-check these against your lesson material for any specific context or nuances!