The 2 types of bone markings being identified would be the opening on the occipitomastoid suture in which the internal jugular veins would travel to carry the blood from one's brain to the heart and the Mandibular condyle of the mandible that would then form the temporomandibular joint.
I think it is A but not 100% sure. Think of an enzyme like a key unlock the lock is the protein. And to activate getting inside your car or house you have to fit the key into the lock.
