Identify the order of the steps that lead from isolation to evolution

The steps of speciation are identified as reproductive isolation and genetic change. These can happen simultaneously or one after the other. This means that the main aim is to have new species through evolutionary changes brought by geographic barriers separating a population or due to behavioral change in a sub-population and even being reproductively isolated. 

answer; ///i believe the correct answer is (aids) acquired immune deficiency syndrome;

the answers are a and c