The plantation workers were on a collision course before the labour officer intervened.

Answer: Option C

Collision : an instance of one moving object or person striking violently against another.
Circuitous : (of a route or journey) longer than the most direct way.
Retaliatory : (of an action) characterized by a desire for revenge.
Conciliatory : intended or likely to placate or pacify.
Perfunctory : (of an action) carried out without real interest, feeling, or effort.

Antonym of Collision is Conciliatory