Four main principles to the theory of evolution

Variation, Heritability, competition, and different survival.

If you are referring to Darwin's Theory...

1.

Individual show variation

2.

Variations can be inherited

3.

Organisms produce more offspring then can survive

4.

Variations that increase success will be more likely to be passed on to future generations

Hope this helps, (:

The correct answer is a. we know this because n (hap) + n (hap) = 2n (dip).