The basic rule for articles in English is that you use “a” for words that begin with consonants and “an” for words that begin with vowels. However, if you are talking about abbreviations, especially in science papers, this basic rule doesn’t work.
The basic rule for articles in English is that you use “a” for words that begin with consonants and “an” for words that begin with vowels. However, if you are talking about abbreviations, especially in science papers, this basic rule doesn’t work.