Consider the reaction that occurs when copper is added to nitric acid.

[tex]\[Cu (s) + 4 HNO_3(aq) \longrightarrow Cu(NO_3)_2(aq) + 2 NO_2(g) + 2 H_2O (l)\][/tex]

What is the reducing agent in this reaction?

A. [tex]\(Cu\)[/tex]

B. [tex]\(NO_3^{-}\)[/tex]

C. [tex]\(Cu(NO_3)_2\)[/tex]

D. [tex]\(NO_2\)[/tex]