The correct answer is C. At the park we saw a unicyclist juggling four bottles.
Explanation:
In grammar a participial phrase is a phrase containing a participial (word ending in -ing or -ed) which function is the one of an adjective or modifier, this means the use of a participial phrase serves to define or modify a noun in the sentence. In this case, the phrase "at the park we saw a unicyclist juggling four bottles" is the only one containing a participle which is the word "juggling" that ends in -ing and acts as an adjective describing and modifying the "unicyclist" which is a noun. In this way "juggling four bottles" includes an -ing word (participle) that describes the "unicyclist" and thus, it is considered as a participial phrase.
