Final answer:
The one requirement for a stocked handwashing sink is soap and water.
Step-by-step explanation:
The one requirement for a stocked handwashing sink is soap and water. According to the CDC's handwashing recommendations, hands should be wet with clean, running water before applying soap. Soap is essential for effectively removing dirt, germs, and pathogens from the hands. Hand sanitizers, gloves, and paper towels are not mentioned as requirements for a stocked handwashing sink.