In which sentence is the participle used correctly?

The sentence that uses the participle correctly is the one that states "Sailing on the open sea, we spotted many dolphins." This construction is effective because the participle "sailing," which describes the action happening in conjunction with the main clause, clearly indicates who is performing the action of spotting the dolphins. The subject of the sentence, "we," is directly related to the action of sailing, establishing a logical and clear relationship between the two actions.

In contrast, the other sentences create confusion about who is performing the action of sailing. For instance, the first sentence leads the reader to believe that "many dolphins" is doing the sailing, which is not accurate. Sentences that lack a clear subject connection weaken the clarity of the message. Thus, the option that maintains the proper subject-verb relationship and uses the participle effectively is indeed the correct choice.