During the Terminal Stance and Pre-Swing Phases of Gait, Knee

During the terminal stance and pre-swing phases of gait, knee flexion occurs _______ from _______________________________.

A) actively; a concentric contraction of the hamstrings
B) actively; an eccentric contraction of the quadriceps
C) passively; a concentric contraction of the singe joint hip extensors
D) passively; the combined motions of hip flexion and ankle plantarflexion