The correct answer is A. Vacuum.
Sound waves are a form of energy that travels through matter in the form of pressure waves. They are produced by vibrating objects, and they can travel through solids, liquids, and gases. However, they cannot travel through a vacuum.
A vacuum is a space that is completely empty of matter. There are no atoms or molecules in a vacuum, so there is nothing for sound waves to travel through. This is why you cannot hear anything in space, even though there are many stars and planets there.
The other options, B, C, and D, are all materials that sound waves can travel through. Water is a liquid, glass is a solid, and hydrogen gas is a gas. All of these materials have atoms or molecules that can vibrate, and this vibration can create sound waves.
Therefore, the only option that sound waves cannot travel through is A. Vacuum.