28)
in some instances, humans breed animals that are close relatives to produce desired traits. this is called

Inbreeding

Inbreeding is the process of mating of individuals or organisms that are closely related through common ancestry, as opposed to out breeding, which is the mating of unrelated organisms. Inbreeding is used to concentrate desirable traits. Mild inbreeding has been extensively used in laboratory for  mice and rats.

sodium i think the chemical element of atomic number 11, a soft silver-white reactive metal of the alkali metal group.

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