All of the following are electromagnetic waves except
a. x rays.
b. sound waves.
c. gamma rays.
d. radio waves.

B. sound waves
Sound waves need to travel through a medium such as a solid, liquid, or gas. The sound waves move through each of these mediums by vibrating the molecules in the matter. This means it isn't an electromagnetic waves but it is a wave, an example of the difference, all electromagnetic waves can travel in a vacuum at the universal speed limit, this is 299 792 458 m/s.

Alinear relationship would look like a straight line on the graph. it could have a positive negative or 0 slope. so it could be a line potentially going in any direction but it must be perfectly straight.