What might engineers use to test a new software design? Simulations. Robotics. Microscopes. Incubators.

sound moves fastest in solids because the molecules are tightly packed and it allows sound to vibrate

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