a rare occurrence的用法和样例：
- Vandalism used to be a rare occurrence here.
- Laughter was a rare occurrence in his classroom.
- This is a rare occurrence as our climate seldom god to extremes.
- This is a rare occurrence as our climate seldom goes to extremes.
- The mystique of the four leaf clover continues today, since finding a real four leaf clover is still a rare occurrence and omen of good luck.