This preference for exogamy，Gutman suggests，may have derived from West African rules governing marriage，which，though they differed from one tribal group to another，all involved some kind of prohibition against unions with close kin. (3+)

　　难句类型：复杂修饰、插入语

　　译文：古特曼表示，这种对于外部通婚的偏爱很有可能缘起于西部非洲制约着婚姻的规定，尽管这些规定在一个和另一个部落群体之间不尽相同，但都涉及到某种对近亲联姻(union with close kin)的禁止。

　　解释：本句有两个插入语，第一个插入语Gutman suggests割裂了主句的主语和谓语。West African rules后跟着两个修饰成分，第一个是分词修饰(governing marriage), 第二个是以which引导的非限定性定语从句，从句中出现了第二个插入语though they differed from one tribal group to another，又割裂了从句引导词与谓语之间的联系。

　　训练：This preference for exogamy，Gutman suggests，may have derived from　West African rules governing marriage，which，though they differed from one tribal group to another，all involved some kind of prohibition against unions with close kin.