The correct option is A overproduction, variations, constancy of population size, natural selection
The sequence proposed by Darwin and Wallace for organic evolution is:
overproduction, variations, constancy of population size, natural selection.
First, the species produces enormous number of offspring which contains variations. Then extra population is eliminated because all the offspring cannot survive because of population stress. At last, the natural selection operates for the survival of the fittest.
So, the correct answer is option 'a'.