Select the best answer to make the statement true, and place the letter of your answer in the space provided.
Code ${ }^{\circledR}$ restrictions for low-voltage remote control systems __________
a. are the same as those for the standard 120-volt system.
b. specify that No. 12 AWG wire be used in the low-voltage part of the circuit.
c. do not exist.
d. are different from those for the standard 120-volt system.