Answer: The sentences that include only prepositional phrases are "There was no one visible; under him, in the water, the dim shapes of the swimmers had disappeared" and "He could see nothing through the stinging salt water but the blank rock".
Explanation:<u></u><u>A prepositional phrase is a group of words introduced by a preposition</u>. Generally, a prepositional phrase also includes a noun or a pronoun. The sentence "There was no one visible; under him, in the water, the dim shapes of the swimmers had disappeared" <u>contains two prepositional phrases: "under him" and "in the water"</u>, which have been introduced by "under" and "in" respectively. Furthermore, in the sentence "He could see nothing through the stinging salt water but the blank rock", <u>"through the stinging salt" is a prepositional phrase since it begins with the preposition "through"</u>.
