Interjections are words or phrases that express strong emotion or sudden feelings. They often stand alone, but can also be used within a sentence.
Here's how "duh" functions:
* Expresses obviousness: It indicates that something is very clear and should be obvious.
* Conveys annoyance: It can also imply frustration or irritation when someone states the obvious.
For example:
* "You didn't know the answer? Duh, it's right there in the book!" (expresses obviousness and annoyance)
* "Duh, I forgot my phone!" (expresses obviousness)