Language Arts:  Prepositions - Tutorial
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How to Identify a Preposition
Rules for Prepositions
The subject and verb of a sentence can be separated by interrupting phrases.
This section will help you identify prepositions and show how they can be used. 
A preposition usually occurs before a noun or pronoun and expresses a relation to another word.
Interrupting Phrases
Prepositional Phrases
The phrase may occur at the  beginning, somewhere in the middle, or at the end of the sentence.  

Formal:

She has much about which to be anxious.
List of Prepositions: click here

Lessons: click here

Language Arts Homepage: click here
Note: Another way to avoid using a preposition at the end of the sentence without sounding overly formal is to revise your sentence with words that generally mean the same thing.
Once you have learned how to identify prepositions, you can identify them in sentences.

Why is this important?   Well, let's say:
across the chair

between the chair

by the chair

to the chair

under the chair

in the chair

up the chair

before the chair
Here is an easy way to identify a preposition.

Let's choose some prepositions and place them in front of the article the and a randomly chosen noun: chair,
The ball was thrown across the street. 
By adding the prepositional phrase across the street -- the reader now has more information about where the ball was thrown.

For a List of Prepositions: click here.
The coach rewarded the team for winning.
A prepositional phrase is a group of words that begins with a preposition and ends with a noun. 

A gerund can function as an object of a preposition
For is the preposition, and winning is the gerund that is acting as an object of the preposition. 

Prepositional phrases can also function as an adverb phrase
in the morning (tells when)

to the store (tells where)

with relish and cheese (tells how)
Example 1:  During lunch break, the incident occurred.

Example 2:  Fred's trophy for perfect attendance was lost.  

Example 3:  The ducks swam in the pond.
Snow-capped mountains, like the Swiss Alps, are quite breathtaking. 
The phrase like the Swiss Alps can be lifted out of the sentence, and the sentence would read:
Snow-capped mountains are quite breathtaking.
The subject (mountains) still agrees with the verb (are).
Interrupting phrases will not affect the agreement between the subject and the verb. 
Interrupting phrases are offset by commas, whereas prepositional phrases usually use a comma when the phrase appears at the beginning of a sentence. 
The ball rolled between the table and the chair. 

Sarah is among the students who will perform at the concert.  

Fred can't choose between joining the Army or the Navy.   
Use between when you are talking about two things or two groups. 

Use among for more than two things.
Even though Army and Navy represent a group, between is acceptable because Fred has two choices.  
It is a commonly known rule: Never end a sentence with a preposition, especially in formal writing.
Preposition at the end:

She has much to be anxious about.  
Revised sentence:

She has many reasons to be anxious.