6. a fine-grained texture most likely formed when a magma cooled

a. deep within the earth.

b. at two different rates.

c. close to the earth’s surface.

d. slowly.

c. close to the Earth's surface

Explanation:

The rocks that form from the cooling magma or lava flows are the igneous rocks. When it comes to their texture they can roughly be divided into two major groups, fine-grained and coarse-grained, further having several sub-divisions as well.

The fine-grained igneous rocks are the ones that are formed either on the surface or very close to the surface. Because the temperature and pressure at this parts is much lower, the magma or the lava cool off very quickly. Because of the rapid cooling off, there is simply not enough time for the crystals to grow larger, so they are very small, often can not even be seen with naked eye.