请教所有格的问题

202. After the Civil War, contemporaries of Harriet Tubman's maintained that she has all of the qualities of a great leader: coolness in the face of danger, an excellent sense of strategy, and an ability to plan in minute detail.

(A)  Tubman's maintained that she has

(B)   Tubman's maintain that she had

(C)  Tubman's have maintained that she had

(D)  Tubman maintained that she had

(E)   Tubman had maintained that she has

In choice D, the best answer, the phrase contemporaries of Harriet Tubman presents a complete possessive without adding an apostrophe (e.g., Tubman's).
            Choices A, B, and C use a redundant possessive:
            contemporaries of Harriet Tubman's. All choices other than D have errors in verb tense. Because the sentence describes essentially simultaneous actions completed in the past, the simple past tense forms maintained and had are required. Thus, the present tense forms has and maintain are incorrect in A, B, and E, as are . the present perfect have maintained in C and the past perfect had maintained in E.

这道题我一开始就排除了D,E就是因为Tubman后面没有's,结果答案的解释却是"Tubman's use " a redundant possessive. 让我不太理解。

我们不是一直都说: a friend of mine, 而从来不会说a friend of I 么？ 这里的所有格到底应该怎么用？

原句中使用了我们经常说的双重所有格：sth of sb's。但是，在GMAT中，双重所有格是错的。

不理解，那请问我的一个朋友用英文应该怎么说呢？

one of my friend : right

one of Jim's friend: wrong ( 总之 of后面的不能有's)