Identify the segment of the sentence which contains a grammatical error.
Startled, he looked around to locate the source of the sharp sound, but would not be finding any.

Correct option is A

Option (a) contains an error.
Explanation:
The phrase "would not be finding" is incorrect tense usage in this context.
The correct form should be “could not find any” or “was not able to find any” for past narrative consistency.
“Would not be finding” is awkward and inappropriate for completed past action.
Grammatical rule used:
In narrative past, use simple past or modal + base form like “could not find” instead of progressive or future conditional tense.
Example:
Correct: He looked around but could not find any clue.
Incorrect: He looked around but would not be finding any clue.