Concept:Proper electrolyte maintenance is the key safety precaution to extend lead-acid accumulator life.Explanation:Topping up should be done with distilled water, not concentrated sulfuric acid H2SO4.Naked flames must be avoided because charging releases explosive hydrogen gas.Direct wire tests on terminals can cause sparks and damage the battery.Keeping the specific gravity of the electrolyte in the specified range prevents plate sulfation.Sulfation reduces capacity and shortens the battery's lifespan.Answer:C. Keeping the specific gravity of the electrolyte within the specified range.