为什么不能是D 语法上有何错误?

题目

为什么不能是D 语法上有何错误?
4.Rita Dove,African American writer and teacher,as poet laureate of the United States from 1993 to 1995.
　　(A) Rita Dove,African American writer and teacher,as
　　(B) Rita Dove was an African American writer and teacher as
　　(C) African American writer and teacher Rita Dove was
　　(D) African American writer and teacher,Rita Dove was
　　(E) An African American writer and teacher,it was Rita Dove

答案

D有双主语的问题,楼上的回答不对,只有当前后句子都是完整句（有谓语动词）的情况下才不能直接逗号连接.
所以是选C吧?