Final answer:
Under the Biological Species Concept, two groups of organisms that cannot produce fertile, viable offspring are considered different species due to reproductive isolation.
Thus option d) Reproductively. is correct answer.
Step-by-step explanation:
According to the Biological Species Concept, two groups of organisms that are unable to form fertile, viable hybrids are considered to be different reproductively. Reproductive isolation means that members of a species cannot mate successfully with members outside their species, thus preventing gene flow.
This reproductive barrier is foundational to the determination of a species, as it emphasizes the ability to interbreed and produce fertile offspring as the criteria for species delineation.
This concept emphasizes the importance of gene flow and reproductive compatibility in defining species boundaries.
Thus option d) Reproductively. is correct answer.