Hint:-In the pollen sac or microsporangium of the anther in the flowering plants, the haploid microspores are formed by mitotic division. Then mitosis produces a two-celled pollen grain that has a small generative cell and a larger vegetative cell. This generative cell undergoes further mitosis to form two male gametes. During which the pollen tube develops from the be vegetative cell and grows through a pore in the pollen grain. Pollen tube contains the vegetative nucleus at its tip and the male nuclei behind it.
Complete answer: The oosphere called ovum or egg cell is the nonmotile female gamete in plants and algae. In flowering plants called angiosperms, the oosphere is a cell in the embryo sac of the ovule. In algae examples, Fucus oogonia protects the oosphere until it is shed into the water for fertilization. The oosphere is a single large-sized cell as it provides the embryo with food during the initial phases of development with thick cytoplasm and various vacuoles inside the cell. The male gametes of angiosperms are pollen grains, which are microscopic single-celled particles with a tough coat and thin cytoplasm and have no vacuoles. Thus, the right option is D.
Note:- The male gametes of angiosperms consist of a pollen grain or a pollen tube with two sperm cells present within. These are derived from a single generative cell, which is formed by meiosis in the microsphere. ( the smaller cell by unequal cell division). The gametes formed are non flagellated and nonmotile throughout the life cycle of angiosperms.