The correct option is B auspicious
The word 'sinister' refers to giving the impression that something harmful is going to happen.
Option A, malevolent refers to having or showing a wish to do evil to others.
Option B, sinful refers to being wicked and immoral.
Option C, auspicious refers to being a sign of future success.
Option D, right refers to being morally good, justified or acceptable.
Thus, according to the meaning, the word 'auspicious' is the opposite of the word 'sinister'.