Answer:
Rock formed by cooling
Step-by-step explanation:
Rock A represents a magmatic rock that was formed by cooling and solidifying the magma that was expelled from a volcano.
The cooling of the magma is capable of generating rocks rich in crystals in its composition. Most crystals are not visible to the naked eye, but make up the rock in its entirety, when cooling occurs on the earth's surface. When cooled inside the earth, magma also forms rocks rich in crystals, which in turn are visible to the naked eye.