To understand the question Co nie przepuszcza dźwięku? it's important to know that przepuszcza means lets through and dźwięk means sound in Polish. The question is asking for something that doesn't let sound through. The most complete answer is Materiał lub obiekt, który jest całkowicie nieprzezroczysty dla dźwięku, nie przepuszcza dźwięku. It means that materials or objects that are completely opaque to sound don't let sound through. They block the sound from passing through. Some examples of materials or objects that don't let sound through are: thick walls, concrete barriers, soundproof doors, or heavy curtains. When sound encounters these barriers, they reflect or absorb the sound waves, preventing them from passing to the other side.