6584. An enquiry was ordered to ascertain the actual cause of the accident.

✅ The correct answer is option A.
Determine : ascertain or establish exactly by research or calculation.

Investigate : carry out a systematic or formal inquiry to discover and examine the facts of (an incident, allegation, etc.) so as to establish the truth.

Discover : find unexpectedly or during a search.

Prove : demonstrate the truth or existence of (something) by evidence or argument.

Ascertain : find (something) out for certain; make sure of.

Synonym of Ascertain is Determine