In an open-chain leg extension, the ___________ rotates around the ______________. In a closed-chain leg extension, the _________________ rotates around the __________________.
A. femur, tibia/fibula; tibia/fibula, femur
B. tibia/fibula, femur; femur, tibia/fibula
C. tibia/fibula,femur; tibia/fibula, femur
D. none of these.