Answer :
The answer to your question would be that the participial phrase in the sentence is the following one: Seeing the massive shark. That is, the correct option would be D.
A participial phrase begins with a present or past participle and it includes objects and modifiers that complete the thought. In addition to this, they always function as adjectives as they add a description to the sentence. In this case, "seeing the massive shark" describes "the divers".