Rocks are classified according to their composition and color.

The sentense is true.

In geology it is called rock to each one of the diverse solid materials, formed by crystals or grains of one or more minerals, of which the solid part of the Earth and other planetary bodies is made. On Earth the crust is made of rock. The study of rocks is called petrology.

Rocks can be classified according to their properties, such as chemical composition, texture, permeability, among others. In any case, the most used criterion is the origin, that is, the mechanism of its formation. According to this criterion, they are classified as igneous (or magmatic), sedimentary and metamorphic, although a class of alteration rocks can be considered separately, which are sometimes studied among sedimentary rocks.

d.

thist title points out that you are explaining the nature of the u.s. government. it is the most specific. a representative government consists of a government where decisions are taken according to a voting system. the most essential aspect of a representative government is found in the different structures where voting rights are granted to different groups of people. for example, voting for governor, mayor, president, local police chief etc.