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).
The definition of straw man argument is to make a argument that wasn't presented, so you're right the answer would be A.
Appreciating nature and things around or just actually look at stuff in a clear light for once.
