The correct answer is option A, meiosis
Reason -
In a meiosis cell division the number of chromosomes usually reduces by half of its original number. It helps in the production of gametes—sex cells, or sperm and eggs. In the phase I of meiosis, diploid cell is formed while in phase II of meiosis, haploid cell is formed. Meiosis produces sex cells which are responsible for causing the genetic variation.