Suppose that you and a friend see brightly colored pigeons like these at a nature park. Because pigeons are usually gray and white, you both wonder where these colors came from. Suddenly, your friend says, "I have a theory. These birds must get their colors from eating food that has the same colors."

all these collisions do one thing, and that thing is explained in the last option. when dusst, rocks and ice collide, they harden and form giant layers of rocks or hard ice.

d)   to harden materials to form different parts of earth’s layers

hope it ,

bioteacher101

cytokinin is what stimulates cell division