The endocrine system produces which are chemical messengers that carry a specific message to certain body cells.

a. hormones
b. dendrites
c. feedback mechanisms

d we did this already

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