A prepositional phrase consists of a preposition and a noun or pronoun object plus the modifiers，if any，of the object．These phrases function as nouns，adjectives，or adverbs．

介词词组是以介词为中心词，加上名词或代词及其（修饰）限定词所构成的词组，在句中往往类似于名词、形容词或副词，可充当状语、定语或补足语。

The letter was under a pile of papers．

From New York to Los Angeles is a long trip to make by bus．

They would like to find an office with fax and co py machines．

The negotiation lasted for an hour，but didn't reach any agreement．