$\begin{array}{1 1} (a)\; \text{Gamete, Zygote, Embryo, Seedling} \\ (b)\; \text{Zygote, Gamete, Embryo, Seedling } \\ (c)\; \text{Seedling, Embryo, Zygote, Gametes} \\ (d)\; \text{Gametes, Embryo, Zygote, Seedling} \end{array}$
