Respuesta :

A preposition is a word governing, and usually preceding, a noun or pronoun and expressing a relation to another word or element in the clause, some examples of preposition words are,
-on
-over
-like
-before 
In this case, the preposition word in the sentence,
The birds gracefully flew through the air, is Through 

Answer:

Through

Explanation:

A preposition is a word that shows a relationship in space or time between two particular objects, people, or places. Prepositions can also indicate a logical relationship between these elements. Prepositions tend to be followed by nouns or pronouns. In this case, the preposition "through" explains the connection between the birds and the air.