How does ornithopod diversity parallel gymnosperm and angiosperm diversity?

a) Ornithopods diversified in the Cenozoic Era along with gymnosperms.
b) Ornithopods diversified in the Mesozoic Era alongside gymnosperms.
c) Ornithopods diversified in the Paleozoic Era, preceding gymnosperms.
d) Ornithopods diversified during the rise of angiosperms.