Answer:
Option D , There is a lack of genetic variation for selection to act upon.
Step-by-step explanation:
According to Darwin's theory of natural selection , when an organism undergo uncontrolled mating or sexual intercourse with other organism of the same species it gets an opportunity to produce offspring of varied genetic characteristics that are more fit to sustain in a given environment depending on the available gene pool . Now, in this case when panthers are killed ruthlessly, the number of panthers will reduce and so the gene pool will also shrink.
Therefore, the mating panthers will not get the benefit of selection as to produce a fit offspring that could sustain in a given environment and hence they would not evolve further.
Thus, option D is correct