A(n)
is a group of organs that work together to perform a common function.
A(n)
y is a group of tissues that work together to perform a common function.
A(n) y is a basic unit of structure and function of all living things.
A(n)
is a group of cells that work together to perform a common function.

i think that the best answer would be c.

tell me if im wrong : )

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