The correct option is
C Fusion of two gametes
Syngamy involves the fusion of male gamete with the female gamete (i.e. the egg). Syngamy results in the formation of a diploid zygote, which is the first cell of sporophytic generation. Zygote then divides and forms a multicellular structure called the embryo.
Hence, syngamy is the fusion between two gametes.
So, the correct answer is C.