Both mechanical and electromagnetic waves are caused by what

Mechanical waves can be classed as elastic waves because their transmission depends on the medium's (water, air etc.) elastic properties. Electromagnetic waves are caused because of the varying magnetic and electric fields. They are produced by the vibration of the charged particles.

adding a(n) to an electric circuit would increase the magnetic field around a wire;

b. solenoid

a solenoid is a type of electromagnet whose purpose is to generate a controlled magnetic field.

if the purpose of the solenoid is instead to impede changes in the electric current, a solenoid can be more specifically classified as an inductor rather than an electromagnet.

answera compound;