Test analysis: this question examines the ability to obtain material information. The material information reflects that the rulers restricted the marriage of the clan in order to strengthen local control, which objectively shows that the clan at that time still had great strength and high social status, so item C is correct; In Qin and Han dynasties, the clan system had not yet formed, so item A was excluded; Item B does not conform to historical facts, so it shall be excluded; Item d is inconsistent with the stem information, so it is excluded.