The correct option is D Both a and c
When fertilization takes place inside the female body, it is called internal fertilization. In humans, the female gamete (egg) remains non-motile whereas the motile male gamete (sperm) is introduced into the female reproductive tract for fertilization to take place. The sperm has to generate energy for the movement of the tail which helps in the motility of sperms for fertilization.
Ovum is larger compared to the sperm and stores food resources and cytoplasmic materials for the formation of the embryo. Since the sperm doesn’t take part in the donation of cytoplasm for the embryo, if the food resource in the ova is depleted by the production of energy for motility, then there won’t be any cytoplasmic content available for embryogenesis. Being non-motile hence allows the cell to store extra nutrients for rapid embryo development as there is no energy utilized for the propulsion of the egg.