If an author refers to "a bird on the wing" when speaking of the freedom a mountain man felt, the author would be promoting... O symbolism
O metonymy
O paradox
O oxymoron
O understatement

symbolism

Explanation:

Birds who fly openly and freely are often the symbol of freedom. This is because birds seem to have no limits, they can go wherever they want and fly where they wish, on the wind they seem free and their wings seem to like to tool to reach their freedom.

The symbol is the element that stands for some other concept or idea. Those are usually signs or marks, sometimes graphic, sometimes, verbal, that represent other meanings. They are created by some specific connection and that connection is known to a certain group of people. That group can read and understand the meaning behind the symbol without further explanation. Symbolism is the usage of the symbol. It is the movement and element of the art in which usage of the symbol is incorporated in the art piece.

b.) one noun is substituted for another with which it is closely associated