Directions: Read the given sentences carefully and select the one that is grammatically correct and error-free. If all the sentences contain errors, select "All are incorrect".

The correct grammatically error-free sentence is: "The sudden downfall of the tech firm had a devastating impact on the local economy."

Detailed Analysis of Options:
1. "The manager asked the employees to submit his reports before the weekend." — Incorrect. The plural noun "employees" requires the plural possessive pronoun "their" rather than the singular "his".
2. "The sudden downfall of the tech firm had a devastating impact on the local economy." — Correct. The sentence is proper in structure, pronoun usage, preposition, and subject-verb agreement.
3. "The research team published a comprehensive report at renewable energy resources." — Incorrect. The preposition "at" is used incorrectly; the standard preposition following "report" in this context is "on" or "about".
4. "The lead actor's performance in both plays were widely praised by critics." — Incorrect. The main subject is the singular noun "performance", which requires the singular auxiliary verb "was" instead of "were".