Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. A. Graves's study provides evidence that isthmus fishes are in the process of becoming geographically isolated. B. Graves's study of mutating isthmus fishes yields results that differ from results of other studies involving allopatric speciation. C. Graves's study of isolated populations of isthmus fishes provides some evidence that allopatric speciation might be beginning. D. Graves's study indicates that when isolated, populations of isthmus fishes register neutral or adaptive mutations.