Question

in order to make an electric current flow, it is necessary to have a copper conductors. b an ammeter. c a difference of potential. d an open circuit.

Explanation:

Electric current flows due to a potential difference. Copper conductors are materials through which current can flow, but they alone don't cause the flow. An ammeter is a device to measure current. An open - circuit doesn't allow current to flow. The driving force for current flow is a difference in potential.

Answer:

C. a difference of potential