Which information determines if a NAVTEX message is to be rejected?

Correct Answer: Option B — Subject indicator (single letter from A to Z indicating the type of message).

The B2 character, a single letter from A to Z, serves as the subject indicator for NAVTEX messages. Operators program their receivers to reject specific categories, such as weather forecasts or navigational warnings, based on these indicators to ensure only relevant safety information is printed for the vessel's current voyage.