$\begin{array}{1 1} \text{a. A cavity in the ovule in which pollen grains are stored after pollination.} \\ \text{b. An opening in the megasporophyte through which pollen tube approaches the egg.} \\ \text{c. Microsporangium in which pollen grains develop.} \\ \text{d. A cell in the pollen grain in which sperms are produced} \end{array} $
