Biology

The correct answer is: D.When populations can no longer interbreed

Explanation:

Speciation occurs when populations of the same species can no longer interbreed and produce fertile offspring, even if they were to come into contact again. This reproductive isolation is the key factor in speciation, leading to the formation of new species.

The other options do not necessarily indicate speciation:

A.When populations no longer look the same: Physical differences may arise, but they do not necessarily lead to speciation unless reproductive isolation occurs....