PLSSS HELP IF YOU TURLY KNOW THISS

A. translates to "how are you"
B. says "I'm good" which is a reply to how are you so it isn't b
C. says "how are you, friend?" and you wouldn't nessecarily call your teach "friend" so the best choice is answer A.
Answer: A. "¿Cómo está usted?"
Explanation:
Answer A means "How are you?" in a formal way. You speak to teachers in a formal manner so this is correct.
Answer B means "I'm good!" This doesn't even mean "how are you?", so this is incorrect.
Answer C means "How are you friend?" Your teacher is not your friend so this is incorrect.