Answer: C) extremely rapid cooling
Step-by-step explanation:
When magma goes through extremely rapid cooling and especially if it did not dissolve enough water into it, it could freeze to glass or the mineral crystals that will be formed will be so small, they will look like glass.
This is because the reactions that occur to create minerals are affected directly by temperature such that if the magma cools down extremely slowly, it will form very large crystals but extremely fast would result in small crystals.