I need some help, this is going to be late.​

gravitational force

Explanation:

since they seem like they are falling, gravity usually pulls them down

i think its gravitational force

positive reinforcement? ?

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.