The correct answer is II and III.
Here's the reasoning:
I. Travel in a vacuum - This is incorrect. Sound waves require a medium (solid, liquid, or gas) to travel through and cannot propagate in a vacuum.
II. Are invisible - This is correct. Sound waves cannot be seen; they are a form of mechanical wave that travels through a medium.
III. Move through water - This is correct. Sound can travel through water, and in fact, it travels faster in water than in air.
So the correct answer is II and III.