Final answer:
The participial phrase "bubbling its way" functions as an adjective.
Step-by-step explanation:
The part of the sentence that functions as an adjective is the participial phrase "bubbling its way". A participial phrase is a group of words containing a participle, which is a verb form that functions as an adjective. In this sentence, "bubbling its way" describes the stream, telling us how the stream is behaving.
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