Nice job on your homework! Your sentence is good. Here are some tips to make your sentences even better:

1. Use "the" before "alphabet": "My favorite alphabet is the letter A."
2. Capitalize letters when talking about them: "A is the first letter."
3. Try to be more specific: "The letter A comes first in the alphabet."

Keep practicing, and you’ll get even better!

~Teacher Cathy

My favorite alphabet is a because a is first of the alphabet

>>My favorite letter is A because A is the first letter of the alphabet.

OR>>My favorite letter is A because it is the first letter in the alphabet.