What chareteristic is used to classify a mammal as a monotremes marispuial or placental mammal

well, i believe that the answer is 2. : 3

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