Answer:
on the shore
Step-by-step explanation:
A preposition is a word or phrase used to indicate when or where something is occurring. So we can rule out the phrases which don't include a preposition (sang songs and the sailor).
A prepositional phrase consists of a preposition and a noun which it is describing. The preposition in this sentence is on and it is describing where the sailor is in relation to the shore. Therefore, on the shore is the prepositional phrase.