How should I write 'Why tranferred' section?

During my high school life, I attended three different schools. On the common app, there is a section that writes the reason why I left my previous school or why I choose to attend school. What I am wonder is should I write this section in essay format or bullet points format?

Are there obvious reasons like your parents moved to a different area so that you had to change schools?

Why did you transfer?

What is the word or character limit on your response?

I moved first school to second school, because first school did not offer many APs. I moved to second school to third school, because I got a green card and I was eligible to attend public school. Word limit is 250.