The seasons on earth are created by the
a. tilt of earth on its axis, and the revolution of earth around the sun.
b. gravitational pull of the galaxy and dwarf planets.
c. location of earth's hemispheres, separated by the equator.
d. location of earth's moon and its gravitational pull.

electrical power

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.