The correct option is C mitotically, mitosis
Mitosis is the equational division of the cell while meiosis is the reductional division. Mitotic division ensures that the ploidy of the cell is maintained in the daughter cells while meiotic division reduces the number of chromosomes in the nucleus to half.
The formation of embryo sac from the megaspore is known as the megagametogenesis. Megaspore is the haploid cell that is formed as a result of meiotic division of the MMC. All the divisions that take place in the process of megagametogenesis are mitotic in nature. Meiosis occurs during the phase of megasporogenesis, which results in the formation of megaspore from the MMC.