Correct answer

Commentary

　Glass is made of sand called silica sand as
the main raw material,
originally, quartz sand has high transparency
it is made of the same ingredients.
Once the silica sand melts at high temperature,
once it becomes liquid and it cools down,
crystal structure collapses
crystal and crystals are depleted.
Then, since there are no obstructions,
light can pass straight through,
the glass looks transparent.