Final answer:
On a guaranteed substitution, the substituted player is required to leave the field immediately. The referee enforces rules but does not decide on who is substituted, and the coach usually decides which player comes off.
Step-by-step explanation:
The subject of the question pertains to rules regarding substitutions in sports, most likely soccer, given the context of the question. When a guaranteed substitution situation occurs, the rule is generally that A) The substituted player must leave the field immediately. This ensures that the game continues in a fair and orderly manner without unnecessary delays. The referee is the official in charge of the game and they enforce the rules, but they do not determine who can make a substitution; that's usually dictated by the rules of the competition or league. In most cases, the coach or manager of the team decides which player is substituted. Rule B), C), and D) do not typically apply in standard substitution protocols.