A. To be placed into a certain classification, a fish must possess all the characteristics of that classification.
Need not be the case since the new fish isn't classified we cannot make a call on the same
B. Physical characteristics, such as skeletons, are scientists' primary means of classifying new species.
This may be one among the classification but not exactly sure about the same
C. Some fish with cartilaginous skeletons are not sharks.
This could be and cannot were not in a positioin to determine the same with the given premise
D. The waters off Papua New Guinea are generally hospitable to eels.
This is a reason that's stated in the passage and can be inferred hence let us hang on to the same
E. A fish cannot be both a shark and an eel.
This is such a compelling choice since the fish isn't classified we are not sure about the same
Hence IMO D