When the concentrations of solutions are the same on both sides of a membrane, the two solutions are

di ko nga alam sagot dyan ii search mo nalang sa ibang application bhie

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

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