Can someone help me plz

Positive I believe... because if you drop it it is negative so picking up a book means positive. thanks for the points though!

Explanation:

a coal burning power plant

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.