What is used to prevent contamination of a potable water system supplying a plumbing fixture such as a galley sink from a backup of sewage sanitary drains?

Correct Answer: Option B — Location of the potable water spigots above the rim of the galley sink.

To prevent cross-contamination, potable water outlets must maintain an air gap. By locating the spigot above the flood rim of the sink, the system ensures that even if the drain backs up, there is no physical path for sewage to siphon back into the potable water supply.