Answer:
A [teacher]
Explanation:
The answer is between a and the. An is only used when the next word (usually a noun) begins with a vowel.
If you mean you are answering a question like "What do you do for a living?" Then you would say "I am a teacher." What you mean is that you belong to a group who makes their living teaching.
If you are answering a question like "Who teaches English 11A?" then you would answer "I am the teacher of English 11A." You are a specific kind of teacher. In your school, likely no one else teaches English 11A. You are the only one
Both are correct. Since you have to choose one answer, I would pick I am a teacher.
