About 450 million years ago, the terrestrial landscape on Earth would have ________. (A) looked very similar to that of today, with flowers, grasses, shrubs, and trees (B) been completely bare rock, with little pools that contained cyanobacteria and protists (C) been covered with tall forests in swamps that would become today's coal (D) had non-vascular, green plants similar to liverworts forming green mats on rock