Final answer:
The correct ending for 3rd declension ablative plural in Latin is -ibus.
Step-by-step explanation:
In the 3rd declension ablative plural in Latin, the correct ending is -ibus. This ending is used for plural nouns and shows that the noun is the object of a preposition or is used in certain grammatical constructions.
For example, the Latin word liber (book) becomes liberibus in the ablative plural form.
Other examples include magister (teacher) becoming magistris and aestas (summer) becoming aestatibus.