Use Of The A And An Questions Medium
The rule for using "A" or "An" before abbreviations is based on the pronunciation of the abbreviation. If the abbreviation is pronounced with a vowel sound at the beginning, then "An" is used. On the other hand, if the abbreviation is pronounced with a consonant sound at the beginning, then "A" is used. For example, we say "an FBI agent" because the abbreviation "FBI" is pronounced as "eff-bee-eye" with an "eh" sound at the beginning. However, we say "a NASA scientist" because the abbreviation "NASA" is pronounced as "nasa" with an "en" sound at the beginning.