大全中的一题，汇总中没找到，前来讨教。

13.   No nation can long survive unless its people are united by a common tongue. For proof, we need only consider Canada, which is being torn asunder by conflicts between French-speaking Quebec and the other provinces, which are dominated by English speakers.

Which of the following, if true, most effectively challenges the author’s conclusion?

(A) Conflicts over language have led to violent clashes between the Basque-speaking minority in Spain and the Spanish-speaking majority.

(B) Proposals to declare English the official language of the United States have met with resistance from members of Hispanic and other minority groups.

(C) Economic and political differences, along with linguistic ones, have contributed to the provincial conflicts in Canada.

(D) The public of India, in existence sine 1948, has a population that speaks hundreds of different, though related, languages.（E）

(E) Switzerland has survived for nearly a thousand years as a home for speakers of three different languages.

答案是E。如果E正确，那D为什么不对？

我选C，因为还有别的原因导致conflicts in Canada，所以减弱文中例子对结论的作用。请各位指教。谢谢！