Choose the most appropriate option to fill in the blank in the given…

The correct answer is Option (3) → unless

Complete sentence: Never maintain an argument with heat and clamour unless you think or know yourself to be in the right. The main clause gives a rule (never argue with heat and clamour). The "unless" clause gives the one exception (when you think or know that you are right).

Option	Meaning and use	Example
(1) while	While shows that two things happen at the same time, or a contrast. The sentence needs a condition, not a time link.	She hummed a tune while she worked.
(2) before	Before shows that one action comes earlier in time than another. "Never argue before you think you are right" gives no exception to the rule.	Wash your hands before you eat.
(3) unless (answer)	Unless means "if not" or "except when". It introduces the only condition under which the main statement does not hold. Deciding clue: the rule opens with "Never", so the blank must bring in the one condition that lifts it.	Do not sign the form unless you have read every line.
(4) because	Because gives a reason. The sentence would then forbid arguing for the very reason that you are right, which makes no sense.	He stayed at home because he was unwell.