Question

what step should you take before charging a battery?
make sure you are the only person in the charging area.
run a test to make sure current battery is below five percent.
pour water into the acid.
check to ensure the ventilation system is working properly.

Explanation:

Battery charging can produce flammable hydrogen gas, so proper ventilation is critical to prevent dangerous buildup. The other options are unnecessary or unsafe: you don't need to be alone, batteries don't need to be below 5% to charge, and adding water to acid causes a dangerous exothermic reaction (acid should be added to water, not the reverse, and this is not a pre-charging step).

Answer:

D. Check to ensure the ventilation system is working properly.