Identify the prepositional phrase in the following sentence: The roads are often impassable in the rainy season, but year-round air and ferry services are available. A) often impassable B) impassable in C) in the rainy season D) but air and ferry services

Prepositional phrases obviously start with a preposition. Having this in mind, the prepositional phrase in this sentence is C. in the rainy season, given that the word in is a preposition.

A is incorrect because that is an adjective phrase (the center of the phrase is the adjective impassable). B is incorrect because those two words don't make a phrase at all. D is incorrect because that would be a noun phrase.