21.While the owner of a condominium apartment has free and clear title to the dwelling, owners of cooperative apartments have shares in a corporation that owns a building and leases apartments to them. (A) While the owner of a condominium apartment has free and clear title to the dwelling, (B) The owner of a condominium apartment has free and clear title to the dwelling, but (C) Whereas owners of condominium apartments have free and clear title to their dwellings, (D) An owner of a condominium apartment has free and clear title to the dwelling, whereas (E) Condominium apartment owners have a title to their dwelling that is free and clear, while

答案是C。感觉前面的their是说那些 owners of condominium apartments，而后面的them是说owners of cooperative apartments。不是指代同一个对象啊？难道代词指代的对象，只要是张德一样就可以啦（都是owners)？不要管具体的逻辑意思？

谢谢指教！