Please answer the following question: Fact 1: Passive immunity lasts only as long as the antibodies survive in body fluids. Fact 2: Factors in Body Fluid Health Potassium and sodium are crucial to the body's fluid balance. Given the two facts above, answer the question "Passive immunity lasts when the antibodies survive in something containing what?" with the following options: - fever - Leptospirosis - resistance - Chlorophyll - potassium - disease - bacteria - parasites
A:
potassium