When a person jumps up he or she is able to come down because of what?

when a person jumps up he or she is able to come down because of the force of gravitation which pulls it back towards the Earth.

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.