The best answer is C.
When the sperm cell meets an egg, a zygote is first formed. A zygote is a single diploid cell. It is created when two haploid cells merge, in this case the sperm cell and the egg.
Haploid cell is a cell that has a single set of chromosomes. The sperm cell and egg are both haploid meaning each has a single set of chromosomes, 23 in number (for humans)
Diploid cell is a cell that has two complete set of chromosomes. In human this will be 23 + 23 to make 46.
The zygote develops into an embryo.