Final answer:
Desmond exhibited resourcefulness by recalling his library card number to return a library book without having the physical card.
Step-by-step explanation:
The subject of the question revolves around identifying a character trait based on a scenario in which Desmond is returning a library book and despite not having his library card on him, he recalls the number from memory to facilitate the return process. The character trait that best fits this description is Resourcefulness, as it illustrates Desmond's ability to effectively solve the situation by promptly providing an alternative (his card number) to the librarian.