In the primary dentition, what percentage of children typically exhibit a 'flush terminal plane' molar relationship?

Studies show approximately 43% of children in primary dentition exhibit a flush terminal plane (straight/vertical distal surfaces of upper and lower second primary molars). About 37% show a mesial step (lower second molar more mesial — favorable for Class I permanent molar). About 15% show a distal step (unfavorable, leads to Class II). Only 5% show an exaggerated mesial step. C (43%) is the correct answer for flush terminal plane.