is it b? please help

Answer:
Yes.
Explanation:
A: You had better not repeat the same mistake again. Makes no sense.
B. You should not repeat the same mistake again. Correct.
C. You could not repeat the same mistake again. Incorrect. We only use this word in phrases....sometimes.
D. You can not repeat the same mistake again. Ircorrect. No spacing Between Can and not.
hope this helps.