Given the task definition and input, reply with output. Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.

When to use a or an before a noun when there are adjectives before that noun? like the following example: An operator pressed the button. should that make: A professional operator pressed the button. An professional operator pressed the button. same for: A Hypertext markup language. An Hypertext markup language. Sometimes it seems a bit confusing, especially when there are more adjectives like: An omen was revealed to the priest. A terrible omen was revealed to the priest. An overwhelming terrible omen was revealed to the priest. What is the rule?.

The article changes based on the word immediately following, not necessarily on the noun. There is no difference in meaning between 'a' and 'an' - the distinction is used to preserve an alternation between vowels and consonants when the sentence is spoken aloud. Be aware that speakers of American and British English observe different rules (mainly because we can't agree on whether to pronounce the letter H or not!) In your example: A Hypertext Markup language. An Hypertext markup language. an American speaker (and, to be honest, most British speakers) would find the first one correct, while an exaggerated aitch-dropper would use the second. In these examples: An omen was revealed to the priest. A terrible omen was revealed to the priest. An overwhelming terrible omen was revealed to the priest. all three are correct as written, whether the speaker is American or British.