Concept:Modal auxiliary verbs show obligation, advice, possibility, or intention based on context.
Explanation:The sentence expresses a strong moral judgment about the speaker's action.
"Should" is used to give advice or express what is right and proper.
Saying "You should be ashamed" means you ought to feel ashamed because your action was wrong.
"Might" suggests only a slight possibility, which does not fit the tone of blame.
"Shall" with "you" is normally used for formal commands or future intent, not for moral disapproval.
"We" does not agree with the subject "You" and creates an ungrammatical sentence.
Therefore, the word that fits naturally and correctly is "should".
Answer:B. should
You should be ashamed of yourself for saying such a thing before the principal.