The correct option is
A Kindly
The word 'oppressive' refers to inflicting harsh and authoritarian treatment.
Option A, gentle refers to having a mild, kind or tender temperament.
Option B, kindly refers to having a warm and affectionate manner.
Option C, smooth refers to being suavely charming in a way that is regarded as possibly insincere.
Option D, orderly refers to being charged with the conveyance or execution of orders.
Thus, according to the meaning, the word 'kindly' is the most opposite in meaning from the word 'oppressive'.