Prepositions of time are essential for discussing when events occur. The most commonly used prepositions of time are at, on, and in. Each has a specific context of use:

At: Use "at" for precise times.
Example: "The meeting starts at 7 AM."

On: Use "on" for days and dates.
Example: "We have a meeting on Monday."

In: Use "in" for months, years, and longer periods.
Example: "I graduated in 2020."

Mastering these prepositions will help make your English sound more natural and improve your communication skills, especially in contexts like the TOEIC test.

ANSWERS: Here are the corrected versions of each sentence using the correct prepositions of time:
1. The train leaves at 9 AM.
2. He was born in March.
3. We celebrate our anniversary on September 15th.
4. The office opens at 8 o'clock.
5. They moved to their new house in 2020.