Choose the most suitable option to replace the highlighted part of the sentence:

Had I been aware of the delay, I will start earlier .

The correct answer is would have started earlier.

Step-by-Step Explanation:

1. Analyze the Sentence Structure:
The given sentence is: "Had I been aware of the delay, I will start earlier ."
This is an inverted form of a Third Conditional sentence (an unreal or hypothetical situation in the past).

2. Understand the Third Conditional Rule:
A third conditional clause expresses a past condition that did not happen and its hypothetical past result.
Standard structure: If + had + past participle, ... would have + past participle
Inverted structure (omitting 'if'): Had + subject + past participle, ... subject + would have + past participle

3. Identify the Error:
The condition clause uses "Had I been aware" (past perfect inverted), so the main result clause must use "would have" followed by the past participle of the verb ("started").
The original sentence incorrectly uses "will start", which violates the grammatical rule for conditional sentences discussing past past possibilities.

4. Evaluate the Options:
- would have started earlier: Correctly uses "would have" + past participle ("started").
- would start earlier: Incorrect because "would + base verb" is used in second conditionals for present/future hypotheticals, not third conditionals.
- had started earlier: Incorrect because it lacks the modal auxiliary verb "would".
- would started earlier: Grammatically incorrect because "would" must be followed by a base verb or "have".

Therefore, replacing the highlighted part yields the grammatically correct sentence: "Had I been aware of the delay, I would have started earlier."