George is lifting weights. he starts by doing biceps curls which involves ____________ his elbows. his elbow is able to bend because the humero-ulnar joint is a ____________ joint. sam is doing leg presses, ____________ his knees as he pushes against the weights. the knee joint is primarily a ____________ joint, though it can act as a condylar joint when flexed. meanwhile, jane is doing "lat pulls" by pulling downward on a weighted bar. this movement involves ____________ of her arms. her shoulder joint is a ____________ joint, allowing a wide range of movements.