What is the most important feed grain for livestock

hay

Explanation:

Feed grains are the most important source of animal feed. The amount of grain used to produce the same unit of meat varies substantially.

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.