The correct answer is: A. Short the load resistor.
To get the Norton current, you have to short the load resistor. This is because the Norton equivalent circuit is a current source in parallel with a resistor. The current source is equal to the short-circuit current of the original circuit, and the resistor is equal to the output impedance of the original circuit.
Option B is incorrect because opening the load resistor will not result in a current source. Instead, it will result in an open circuit.
Option C is incorrect because shorting the voltage source will not result in a current source. Instead, it will result in a short circuit.
Option D is incorrect because opening the voltage source will not result in a current source. Instead, it will result in an open circuit.
Option E is incorrect because it is not one of the possible answers.