Signal must travel from one animal to another, and the receiver of the signal should respond in some way. This is called . a.
competition
c.
food and water
b.
courtship
d.
communication

the earth is thought to have been formed about 4.6 billion years ago by collisions from a cloud of hydrogen, helium, rock, ice and other materials. these were pulled together by gravity to form objects in and around earth like- asteroids and small early planets called planetesimals.

so, the best possible answer to this question will be option d- to harden materials to form different parts of earth’s layers