The two principal ways to describe earth’s structure are based on the
a)
chemical composition and thickness of layers
b)
chemical composition and mechanical properties of layers
c)
mechanical properties and thickness of layers
d)
the composition and viscosity of minerals
not a

A) chemical composition and thickness of layers is the correct answer

Explanation:

The two principal ways to describe Earth’s structure are based on the  chemical composition and thickness of layers.

The Earth has three main layers and the structural composition of the earth is divided into three layers

Thus the Earth is a layered arrangement, which is observed according to its various chemical composition and thickness.

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.