Answer :
I think it’s prepositional phrase I might be wrong and sorry if I’m wrong
The function of "at the joke" in the sentence is :
2. Adverb Phrase
"Phrases"
The sentence is the kids were laughing at the joke their father told the function of "at the joke" in the sentence is adverb Phrase.
An adverb phrase is basically a gather of two or more words that work as an verb modifier in a sentence.
It is just as an qualifier can adjust a verb, descriptive word or another intensifier, an qualifier express of more than one word can encourage portray a verb, intensifier, or descriptive word.
Thus, the correct option is 2.
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