Using articles with abbreviations and acronyms:
One of the most often asked questions about grammar has to do with the choice of articles a, an, the to precede an abbreviation or acronym. Do we say an FBI agent or a FBI agent? Although "F" is obviously a consonant and we would precede any word that begins with "F" with "a," we precede FBI with "an" because the first sound we make when we say FBI is not an "f-sound," it is an "eff-sound." Thus we say we're going to a PTO meeting where an NCO will address us. We say we saw a UFO because, although the abbreviation begins with a 'U," we pronounce the "U" as if it were spelled "yoo." Whether we say an URL or a URL depends on whether we pronounce it as "earl" or as "u*r*l."