Skill 2 : Objects of Preposition

An object of preparation is a noun or pronoun that comes after a preposition such as in, at, of, by, behind and on to form a prepositional phrase.

The trip (to the island) (on Saturday) will last (for three hours).

This sentence contains three objects of prepositions. Island is the object of the preposition to; Saturday is the object of preposition on; how is the object of the preposition for. 
An object of a preposition can cause confusion in the Structure section of the TOEFL test because it can be mistaken for the subject of a sentence.
Example :
To Mike.........was a big  surprise.

1. really
2. the party
3. funny
4. when

In this example, you should look first for the subject and the verbs. You should notice the verb was and should also  notice that there is no subject. Do not think that Mike is the subject; Mike is the object of the preposition to, and one noun cannot be both subject and an object at the same time. Because a subject is needed in this sentence, answer (2) the party, is the best answer. Answer (1), (3) and (4) are not correct because they cannot be subjects.

The following chat outlines the key information that you should remember about objects of prepositions.
"A preposition is followed by a noun or pronoun that is called an object of the preposition. If a word is an object of preposition, it is not the subject."