Final answer:
Ampère's law states that the line integral of the magnetic field around an electric current is proportional to the current. It must be integrated along the path of a closed physical conductor, such as a wire.
Step-by-step explanation:
Ampère's law states that the line integral of the magnetic field around an electric current is proportional to the current. The circle on the integral symbol indicates that the magnetic field must be integrated over a closed path. In this case, the correct option is c - Ampère's law must be integrated along the path of a closed physical conductor, such as a wire.