C

Class III facemask protraction aims the elastics downward and forward so the line of force passes near the maxillary centre of resistance. Clinical and biomechanical studies typically apply the elastics at ≈30° below the occlusal plane; the closest choice given is the 35-40° downward vector (option C) [Ngan et al., 1997, PMID 9573887; Hong et al., 2005, PMID 15898388].