a. A structure in pteridophytes formed before the thallus develops

b. A sporophytic free-living structure formed in pteridophytes

c. A gametophyte free-living structure formed in pteridophytes 

d. A primitive structure formed after fertilization in pteridophytes

A)Correct option – C

B) Explanation of correct option –

●Prothsllmus is usually the gametophyte stage in the life of a fern or other pteridophyte.

●Develops from a germinating spore.