Correct the underlined part of the following sentence if necessary: Have you been more careful, the accident could have been averted. Which of the given options best replaces the underlined words to make the conditional sentence grammatically correct?

Introduction / Context:
This question tests your understanding of conditional sentences in English, particularly the third conditional which talks about unreal past situations. The sentence given is Have you been more careful, the accident could have been averted. We must choose the correct introductory phrase that makes the sentence grammatically correct and meaningful in standard English usage.

Given Data / Assumptions:

The speaker is referring to a past situation where the accident actually happened.

The intended meaning is that if the person had been more careful in the past, the accident would not have occurred.

The main clause uses the form could have been averted, which matches a hypothetical result in the past.

The underlined phrase before the comma needs to be replaced with an appropriate conditional clause starter.

Concept / Approach:
The standard third conditional structure in English is If + past perfect, would or could have + past participle. The past perfect form of be is had been, so the full correct clause is If you had been more careful, the accident could have been averted. When we drop if, we invert the subject and auxiliary to form Had you been more careful, which is a common formal variant. Thus Had you been is the correct phrase to express a past unreal condition consistent with could have been averted in the result clause.

Step-by-Step Solution:

Verification / Alternative check:
To verify, insert each option into the sentence and see which version sounds grammatically correct and matches the intended hypothetical meaning. If you have been more careful refers to a continuing state and does not fit the completed past accident. If you could have been more careful is also incorrect because could have already appears in the result clause and doubling it is not idiomatic. Only Had you been more careful, the accident could have been averted expresses the correct past unreal condition and results in a fully grammatical sentence.

Why Other Options Are Wrong:

Have you been introduces a question like Have you been more careful but not a conditional clause, so it is not appropriate here.

If you have been uses present perfect, which is not suited for describing a completed past situation that can no longer change.

If you could have been is structurally awkward and does not produce a standard third conditional form when combined with could have been averted in the main clause.

Common Pitfalls:
Students often confuse different conditional patterns and mix verb tenses. Another common issue is forgetting that after dropping if in a conditional with had, we must invert the subject and auxiliary, producing Had you been instead of You had been. Reviewing conditional forms with several examples helps prevent these typical errors and improves accuracy in sentence correction questions.

Final Answer:
The correct phrase that should replace the underlined part is Had you been.