Q) What is a usual name for electromagnetic waves that travel through space?
A) Radio waves
It is often helpful to eliminate the obvious wrong answers when faced with a question you are unsure of.
A. Gravity waves - Gravity (what casues the apple to fall from the tree) is not an electromagnetic phenomena.
B. Sound waves - Sound (what you hear when a dog barks) is not an electomagnetic related.
C. Radio waves - Correct, radio waves are electromagnetic phenomena.
D. Pressure waves - Pressure waves is a term used when discussing sound waves. This is a red-herring answer that doesn't relate to radio or electromagnetic waves.