B. It traps heat and warms up our planet.
The "medium" is the substance or material that carries a mechanical wave. One of the most important things to remember about waves is that they transport energy, not matter. This makes them different from other phenomenon in physics.
For simple definitions, visit the following website:
https://www.ducksters.com/science/physics/waves.php
B) electron microscopes focus beams of light using magnetic fields
In general, yes it is true that Enzyme molecules react with reactants to produce substrates, but it should be noted that this is not always necessarily the case.