The correct option is
C Regular
The word 'sporadic' refers to something that occurs at irregular intervals or only in a few places.
Option A, spreading easily refers to something that extends over a large or increasing area.
Option B, inciting refers to the act o encouraging or stirring up violent or unlawful behaviour.
Option C, regular refers to something that recurs at uniform intervals.
Option D, uncommon refers to something that is unusual or out of the ordinary.
Thus, according to the meaning, the word 'regular' is the most different in meaning from the word 'sporadic'.