I'm assuming you mean tropes, and it's because the original story tellers used three, leading to story tellers after that to copy them and use the rule of three, and so it just became a normal thing.
Mary -Queen of Scots, French queen- cousin to Elizabeth 1st of England
<span />
1.the average class size at Harbor Elementary School is 32.
2.The National Education Association recommends a class size of 23.
3. She taught sixth-grade students for 12 years.
Hope this helps:)
