Right option is (b) From lower back to a knee
Easiest explanation: The sciatic nerve begins from the lower back and then moves down to the legs. Sciatica is a condition where the person feels pain originating from their lower back and going down to the legs. Since the pain originates from the lower back, placing the electrodes from the lower back to the knee should give an initial assessment. Depending on the extent of the pain, the second electrode may be placed below the knee.