A participle is that form of the verb which partakes of the nature both of a Verb and of an Adjective.
A participle phrase will begin with a present or past participle. If the participle is present, it will dependably end in ing. Likewise a regular past participle will end in a consistent ed.
Since, all phrases require two or more words, a participle phrase will often include objects and/or modifiers that complete the thought.
Participle phrases always function as adjectives,adding description to the sentence.
In this case,
Option B is correct. The present participle phrase, 'wagging its tail' describes the noun 'pit bull'.
Option A is incorrect because there isn't any participle. 'Risked' is a verb.
Option C is incorrect because it is a gerundial phrase acting as an object of the verb 'risked'.
Option D is incorrect as both the participle and noun, that it modifies, have been punched together.