Sexually reproducing multicellular animals start their development form
A.Gastrula
B.Morula
C.Unicellular zygote
D.Ova

Hint:A tissue, organ, or organism made up of many cells are called multicellular. Animals, plants, and fungi are multicellular organisms. Generally, different cells have various functions. In contrast, unicellular or single-celled organisms are much smaller in size and much less complex because they consist of only one cell that can sense their environment, collect nutrients, and reproduce asexually.

Complete answer:Sexual reproduction involves the formation and fusion of gametes. The fusion of gametes leads to the formation of unicellular zygote. This unicellular zygote is universally present in all sexual reproduction organisms. Zygotes are an important link to ensure the continuity of species between one generation of organisms and the next. Every sexual reproductive organism, including humans, begins life with a single cell, the zygote.
The zygote contains all the necessary factors for development, but they only exist as a coded instruction set, located in the chromosomal genes. In fact, the genes of the new zygote are not activated to produce proteins until several cells have divided. During the cutting process, the relatively large zygote is directly subdivided into many smaller cells of regular size through the process of mitosis (normal cells proliferate through division). These smaller cells are called blastomeres and are suitable as early building units for future organisms.
Thus the option (C) is Unicellular zygote, correct .

Note:In humans, identical twins develop from a zygote, which splits into two independent cell clusters at a relatively early stage of their growth. These two qualities, which are genetically identical to each other, continue to become embryos. In contrast, fraternal twins develop from two separate fertilized eggs (two separate eggs fertilized by two different sperm).