Fill in the blanks with the appropriate answers.
The presence of electrically heated pipelines, vessels, or both, shall be evident by posting of appropriate ________ signs or markings at intervals not exceeding ___ along the pipeline or vessel and on or adjacent to equipment in the piping systems that require periodic servicing.
A) warning / 10 ft
B) danger / 15 ft
C) caution / 20 ft
D) none of the above