Answer:
Option-D
Explanation:
There are many ways to define a species on the basis of the phylogeny, morphology and biological relationships.
The species according to the biological species concept are the organisms which can interbreed and produce the fertile offsprings but show reproductive isolation from other species.
In the given question, the modern humans and Neanderthals showed no gene flow that is they are not able to reproduce between them or we can say that they were reproductively isolated from each other. Therefore they can be classified according to the biological species concept.
Thus, Option-D is the correct answer.