$\begin{array}{1 1} (a)\; \text{Gamete formation, fertilization, zygote, embryo} \\ (b)\; \text{Embryo, zygote, fertilization, gamete formation} \\ (c)\; \text{Fertilization, gamete formation, embryo, zygote} \\ (d)\; \text{Gamete formation, fertilization, embryo, zygote} \end{array}$
