单选题 Freeman and slave, A(patrician and plebeian), lord and serf, guild-master and journeyman, in a word, B(oppressor and oppressing), stood in constant opposition to one another, carried C(on an uninterrupted), now hidden, now open fight, a fight that each time ended, either in a revolutionary reconstitution of society at large, D(or in the common ruin of) the contending classes.