Convert the sentence provided below from its passive voice structure to an active voice structure: Rare minerals are known to hav…

Question

Convert the sentence provided below from its passive voice structure to an active voice structure:

Rare minerals are known to have been secretly extracted from the site by unauthorized workers before the inspection.

1. A. Unauthorized workers extracted the rare minerals before inspection.
2. B. The site was secretly mined before the inspection.
3. C. Unauthorized workers are known to have secretly extracted rare minerals before inspection. (Correct answer)
4. D. The minerals had been extracted prior to inspection.

Correct Answer

Option C — Unauthorized workers are known to have secretly extracted rare minerals before inspection.

Detailed Solution & Explanation

The correct answer is Unauthorized workers are known to have secretly extracted rare minerals before inspection.

Key Points

• Two layers must be handled: the reporting frame "are known to" and the inner passive "to have been extracted by unauthorized workers".
• Converting to the active voice moves unauthorized workers into the subject position and turns *to have been extracted* into to have extracted.
• Crucially, the frame "are known to" must be retained — it reports what is understood rather than asserting it as established fact.
• Options A and D drop that frame and state the extraction outright; option B changes the subject to the site and loses the agent entirely.

Additional Information

• Reporting frames such as *is known to, is said to, is believed to, is reported to* carry an evidential hedge, and removing one strengthens the claim beyond what the original said.
• The pattern "X is known to have done Y" is the active counterpart of "It is known that X did Y" — both preserve the hedge.
• In voice conversion, preserve tense, aspect and modality; only the grammatical roles of subject and object are meant to change.