Latin-derived nouns ending in -um change to -a in the plural form.
Um is regular. It follows the Latin -a rule.
Use plural verbs: "The a are ready" (not "is ready").
Yes. The plural a is standard across all English variants.
The word um follows the standard English pluralization rule. When forming the plural, um becomes a. This follows the Latin -a pattern, which is one of the most common plural rules in English.
Understanding why um becomes a helps with spelling and pronunciation. Latin-derived nouns ending in -um change to -a in the plural form.
When using a in writing, remember that it functions as a plural noun in sentences. It pairs with plural verbs and pronouns. For example: "The a are ready" (not "is ready"). This subject-verb agreement is essential for grammatical correctness.