Cognitive scientists argue that the ability to recognize oneself in a

Cognitive scientists argue that the ability to recognize oneself in a mirror—an ability limited to humans, apes, and perhaps to dolphins as well—is an indication of self-awareness.

A. the ability to recognize oneself in a mirror—an ability limited to humans, apes, and perhaps to dolphins as well—is an indication of : Here it should be "dolphin" instead of "to dolphin" . Also using "and " and "as well" is redundant. Eliminate A

B. the ability to recognize oneself in a mirror—an ability limited to humans, apes, and perhaps dolphins—is an indication of : Correct

C. the ability to recognize themselves in a mirror—an ability limited to humans, apes, and perhaps to dolphins as well—is an indication for : " Indication of " is the correct idiom in this context. Also all the same errors in A are repeated. Using "themselves" here is not correct as it may refer to "Cognitive scientists" also. Eliminate C

D. recognizing oneself in a mirror, as do humans, apes, and perhaps dolphins as well, is an indicator for : " Indication of " is the correct idiom in this context. And and as well is redundant. Eliminate D

E. recognition of oneself in a mirror—an ability limited to humans, apes, and dolphins perhaps—is used as an indicator for " Indication of " is the correct idiom in this context. Eliminate E