The Rh factor identifies the presence of the rhesus protein in blood. The Rh factor can be represented by a + or – sign. It is important to know the Rh factor because just like how the antigens on the blood must be compatible, the rhesus protein in blood must also be compatible.
If a person has Rh+ blood they can receive blood.
If a person has Rh- blood they can receive blood.

what are the awnser choices? i mean, without choices, it is an incompleat

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