Which of the following statements about ohm’s law is true?
a. to increase the current, decrease the resistance.
b. keeping the same voltage and decreasing resistance decreases the current.
c. ohm’s law relates power, current and resistance.
d. increasing the voltage decreases current if resistance stays the same.

To increase the current, decrease the resistance.  

Explanation:

Ohm's law relates the current, resistance and the voltage. This law states that "the potential difference or the voltage across the ends of any conductor is related directly to the current flowing through it". The mathematical relationship is given by :

V = I × R

Where

R = resistance of the circuit

The current is inversely proportional to the resistance of the circuit. Hence, the correct statement about the Ohm's law is (a) " To increase the current, decrease the resistance".  

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.