The knee is close-packed in extension, when the ligaments are maximally elongated or taut. The joint architecture is such that knee extension causes the points of bony attachment of the joint's major ligaments to move further apart. Therefore, response 'b' is correct. In this part of the range of motion, the elongated ligaments develop an elastic force like that in a stiff rubber band. This force approximates the joint surfaces; it pulls the articular surfaces close together in a "close-packed" position.

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