To test the validity of Kirchhoff's loop rule in a circuit with a battery and multiple resistors connected in series, you would want to verify that the total voltage provided by the battery is equal to the sum of the voltage drops across each resistor in the loop.
Therefore, the correct answer is:
Use a multimeter to test the voltage across the battery and see if it is equal to the sum of the voltages across each resistor.
This approach directly aligns with Kirchhoff's loop rule, which states that the sum of the potential differences (voltages) around any closed loop in a circuit must equal zero. In practical terms, this means the voltage supplied by the battery should equal the sum of the voltages across all resistors connected in series.