Answer:
On the bike.
Preposition - On
Object - bike
Step-by-step explanation:
A prepositional phrase is demonstrated as the modifying phrase that consists of a preposition, its object, and any/or modifiers of the object. These phrases function as adverbs or adjectives in the sentence.
In the given sentence, the prepositional phrase is 'on the bike' which comprises of the preposition 'on', the object 'bike', and the modifier 'the.' It is functioning as an adjective in the sentence because it modifies the noun 'our walk.'