Final answer:
In the context of the 'Warriors' series by Erin Hunter, it is true that a cat must mentor at least one apprentice before becoming a deputy. This is stipulated by the 'Warrior Code', which governs the conduct of the feral cats in these books.
Step-by-step explanation:
The statement that a cat cannot be made deputy if they have not mentored at least one apprentice is true. This rule is part of the fictional universe found in the 'Warriors' series of novels by Erin Hunter, which depicts a society of feral cats living in four Clans. In these books, the Clans have a specific set of laws known as the 'Warrior Code,' which dictates that in order to be considered for the position of deputy, a cat must have mentored at least one apprentice. This is to ensure that they have sufficient experience in teaching and leadership before taking on the deputy role. The 'Warrior Code' is central to Clan life and the development of its members, often playing a crucial role in the storylines of the 'Warriors' books.