Here are the correct answers for the passage:

1. **A. over**
2. **B. an**
3. **C. the**
4. **D. Moreover**
5. **B. which**

So the completed passage reads:

"Education in Vietnam has changed a lot **over** the years. A long time ago, students studied in simple classrooms with only a few books and **an** chalkboard. They often had to study by the light of oil lamps at home. However, today’s schools are much better equipped, **the** help to support students’ learning. Many have computers, libraries, and science labs. Because of these improvements, students can learn more effectively, **Moreover**, the subjects taught in schools have expanded to include technology and foreign languages, preparing students for the future. Although there are still challenges, like crowded classrooms, these changes have helped many students gain better **which** in life."