Brown bears and polar bears are separated by geographical area. Is this postzygotic or prezygotic?

Prezygotic mechanisms include habitat isolation, mating seasons, "mechanical" isolation, gamete isolation and behavioral isolation. Postzygotic mechanisms include hybrid inviability, hybrid sterility and hybrid "breakdown."

Explanation:

if your own plato the answer is b. the fern transitioned from sporophyte generation to gametophyte generation.