D. All of these
Explanation:
On the basis of megaspores contributing to the development of embryo sac, a number of mitotic divisions occur in the functional megaspore. There are three types of embryo sacs:
i. Monosporic embryo sac: In this type of embryo sac, out of the four megaspores, one megaspore at the chalazal side takes part in the formation of the embryo sac. The nucleus divides three times to form 8 nuclei. This type is called the Polygonum type.
ii. Bisporic embryo sac: In this type of embryo sac, two megaspores take part in the formation of the embryo sac. The nucleus of two megaspores undergo two mitotic divisions and the resulting embryo sac is 8 nucleate.
iii. Tetrasporic embryo sac: In this type of embryo sac, all four megaspores take part in the formation of the embryo sac. All the four haploid nuclei remain in a common cytoplasm and forming a coenomegaspore. The final organization of the embryo sac is 8 -nucleate. Hence, the 8-nucleate embryo sac can be monosporic, bisporic, and tetrasporic.