The correct option is C Meiosis
In meiosis, a double set of chromosomes (diploid) is reduced to a single set of chromosomes (haploid) gametes. When these combine in sexual reproduction, the resulting zygote is a diploid. In this way, the chromosomal number of the species is conserved during sexual reproduction.
Mitosis produces cells having same number of chromosomes as the parents. Fission and regeneration are asexual methods of reproduction.