When the Earth cooled from being hot, all the iron and nickel was concentrated inside the Earth forming the inner two layers, inner solid core and outer liquid core. Then with the passage of time the Earth solidified gradually and the mantle solidified and now at this stage the Earth's crust, the outer most part of the Earth, looks like it's final product (the way it does now).
Evaluating everything you read, hear, and see in the media
Answer is A just took the test.
