The answer would be "C. Interbreeding between two populations would be impossible" Species become a species when it can reproduce with another animal of the same species and produce fertile offspring, while it can't do this with other animals.
Answer:
The answer is if the niches of two organisms were moved to the other ecosystem they would compete with one another for the same food and other resources in the environment. Eventually, one species would be likely to outcompete and replace the other.
I think the answer is D. ( or supported by observations ). Because theories change over time, they both NEED to be proven, they do NOT go off of consensus, but they do NEED to be supported by observations.
I hope this helps.