如果此刻一群南飞过冬的大雁从头顶飘过，

　　你会是什么感赶脚儿。

　　2010年春天，一头灰鲸出现在以色列地中海海岸，

　　200年来一直生活在太平洋的灰鲸首度出现在北大西洋，

　　它在北大西洋的首秀可谓是引起了一阵轰动，

　　没有什么能够阻挡它们向自由前进的步伐。

　　动物出现在他们原本不该出现的地方，不仅只有此一例，最近几年北大西洋一种叫做北鲣鸟(Northern gannets)的物种也时不时地在加尼福尼亚海岸遛个弯。

　　动物也疯狂！

　　以下是选自《华盛顿邮报》的这篇文章，就专门讲述了生物界的这种融合趋势

　　一起来来读读吧~

　　One example the authors point to is the Great American Biotic Interchange, which occurred several million years ago when the isthmus of Panama formed, allowing land animals a bridge to cross between North and South America. As the authors note, the fossil record indicates that in this case, mammals from North America invaded South America and outcompeted many of the native species there for resources. This type of outcome is a potential concern with species crossing from the Pacific to the Atlantic, and vice versa.

　　Additionally, introducing new predators into an area where they didn’t previously exist can “change food web dynamics profoundly,” Laidre pointed out. There could be genetic changes within migrating populations, as well. One consequence could be some species or subspecies could eventually be genetically phased out of existence, suggested Ryan Terrill, a Ph.D. candidate at Louisiana State University’s Museum of Natural Sciences, who served as a peer reviewer on the paper. On the other hand, this type of mixing could add genetic diversity to small subpopulations, which could be a good thing, said Laidre.

　　Which of the following best summarizes the above paragraphs?

　　A) Species migration may cause food shortage to the native species.

　　B) Some species or subspecies could be phased out of existence after migrating to a new environment.

　　C) Species migration may help mixing up the native species with the migrating species.

　　D) Species migration may cause problems to both the migrating group and the native species. However, it may increase genetic diversity to small subpopulaitons

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