Which of the Cause(s) Variation in the Genetic Material of Progeny?

Which of the following cause(s) variation in the genetic material of progeny?
1. Sexual reproduction
2. Asexual reproduction
3. Mutations
4. Epigenetic changes
Select the correct answer using the code given below.
(a) 2 only               (b) 1, 2 and 3                (c) 1, 3 and 4                    (d) 1 and 3 only