An or A?
https://www.grammar-monster.com/lessons/an_or_a.htmAn and a are easy to mix up. Use 'an' when the next word starts with a vowel sound. Use 'a' when it starts with a consonant sound. The word sound is important. Some abbreviations that start with consonants start with vowel sounds (e.g., RTA, NTU) and vice versa.