As you move toward the center of the earth from the surface, the a) pressure decreases b) percentage of metal decreases c) layers become more solid d) pressure increases explain how you got your answer!

As you move toward the center of the Earth from the surface, the pressure increases.
Just think about it. It's like water. The deeper you go in a pool or ocean, the more dense it is. That's because the pressure is increasing. 
Same goes for the earth. The farther down you do, the more dense it is.

What is the gold assay