71.距下關節 (Subtalar joint) 作什麼動作時會鎖住 (lock) 橫跗關節 (transverse tarsal joint) 讓足部產生堅硬性 (rigidity)，而形成一穩固的槓桿有利推進 (push off)？ (A) 蹠曲 (plantar flexion) (B) 背曲 (dorsiflexion) (C) 內翻 (inversion) (D) 外翻 (eversion)