answer: C
A participial phrase consists of a participle plus modifiers such as an ‘-ing’, ‘-ed’ and so on
in the following sentence The broken vase, purchased by my grandmother, was suddenly falling to the floor, smashing into pieces, the participial phase is ‘purchased by my grandmother’ because you can find that the above phrase has as verbal ending of ‘-ing’. In addition to this it must not be forgotten that a participle phrase will act as an adjective in any sentence