Over the last century, paleontologists have used small differences bet

Paleontologists have used small differences between fossil specimens to classify triceratops into sixteen species.
The specimens used to distinguish eleven of the species come from animals that lived in the same area at the same time.

Conclusion: This classification is unjustified.

The conclusion is drawn based on the observation that 11 of the species come from animals living in the same area at the same time. This seems to indicate that the classification is unjustified. It seems that 11 is too many species from the same area at the same time though the argument doesn't state it explicitly.

Which of the following will help conclusion be properly drawn i.e. which of the following will justify the conclusion?

(A) Not every species that lived in a given area is preserved as a fossil.

Doesn't help our conclusion. Doesn't say why our current classification is not justified.

(B) At least one individual of every true species of triceratops has been discovered as a fossil specimen.

Again, doesn't tell us that our current classification is not justified.

(C) No geographical area ever supports more than three similar species at the same time.

Correct. We found 11 species in the same area at the same time. But no area supports more than 3 at the same time. So our classification is not justified,

(D) In many species, individuals display quite marked variation.

Our species are quite similar. Many species are quite dissimilar. This doesn't mean our classification is wrong. It doesn't say that the animals belong to different species only if they are quite dissimilar.

(E) Differences between fossil specimens of triceratops that came from the same area are no less distinctive than differences between specimens that came from different areas.

If anything, it helps to say that our classification is justified. Specimens of different species are quite distinctive.

Answer (C)