You … have walked home alone so late at night.

Analyze the question

The sentence is: "You ___ have walked home alone so late at night." It uses a modal verb followed by "have + past participle" (have walked). This structure refers to a past action and expresses criticism, advice, or regret about it.

Explain the concept

Modal perfect forms express judgments about past events:

• ought not to have + past participle means it was wrong or unwise to do something, but it was done. For example, "You ought not to have lied."
• should not have + past participle has a similar meaning.
• need not have + past participle means something was unnecessary, but it was done. Note that "need" here takes no "to" after it.

Check each option

• A. would not have walked: This expresses a hypothetical, such as "I would not have walked home alone." It doesn't fit as advice or criticism directed at "you" in this way.
• B. might not have walked: This expresses possibility, such as "You might not have walked, so we don't know." It doesn't give the sense of disapproval.
• C. ought not to have walked: This is correct. It expresses disapproval, meaning it was unwise or wrong to walk alone so late at night.
• D. need not to have walked: This is grammatically wrong. The correct form is "need not have walked," with no "to."

Answer

The correct option is C. ought not to. The full sentence is "You ought not to have walked home alone so late at night."

Exam tip

Remember that "ought" is always followed by "to", while "need" as a modal is never followed by "to." When a sentence has "have + past participle" and expresses disapproval of a past action, look for should not / ought not to.