$\begin{array}{1 1} \text{a. A structure in pteridophytes formed before the thallus develops} \\ \text{b.A sporophytic free living structure formed in the Pteridophytes.} \\\text{c.A gametophyte free living structure formed in Pteridophytes.} \\ \text{d. A primitive structure found after fertilization in Pteridophytes.}
\end{array} $
