The given sentence is a phrase and not a clause.
The sentence provided, 'The hippopotamus, an extremely dangerous and highly aggressive animal, will attack if it is provoked or feels threatened,' is a phrase and not a clause. A phrase is a group of words that does not contain both a subject and a verb, while a clause is a group of words that contains both a subject and a verb. In this sentence, there is no finite verb, so it is not a clause.
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