What was the key for plants to conquer land?

A  The ancestral green algae developed into mosses that were less well adatped to dry conditions. A cuticle and vascular systems in tracheophytes and dispersal strategies (multicellular gametangia, and multicellular embryos) as found especially in flowering plants (Angiosperms), allowed plants to create the dominant forms we see today.

B  Plants conquered land early before there were animal predators, and what we see today is actually the least diversity of plant life the planet has seen.

C  Plants could only really dominate land after asteroids hit earth and wiped out dinosaurs that were grazing on plants.