Answer:
option A. the factors separate
Explanation:
The Mendel referred alleles as factors. Mendel was unaware about gene but he knew that there are two factors for a single character. The single factor gets transferred from each parent. The gene contains two alleles/factors. The alleles/factors from both mother and father separates at the time of formation of gametes. These gametes from both parents containing alleles/factors recombines and thus forming a zygote.
Thus, factors separate during gamete formation. So, option A is correct.
