What structures might be found on the underside of fern leaves?

a. seeds
b. pollen
c. spores

The correct answer would be - spores.

Explanation:

Ferns have special leaves called fronds. Their spores are enclosed in special structures called sporangia, which are dots or clusters that found on the underside of fern fronds.  

The sporangia have spores that are present with caps called indusia until spores reach maturity. Indusia propel the spores from fern plants forcefully when it burst open. If the spores land in a favorable environment they produce second-generation prothalli.

Thus, the correct answer would be spores.