In the Following Redox Reaction Which Element Is Being Oxidized $\rightarrow$

In the following redox reaction which element is being oxidized?

Cu(s) + 4 HNO₃(aq) $\rightarrow$ Cu(NO₃) ₂ (aq) + 2 NO₂

A) Cu
B) H
C) N
D) O
E) none of these (g) + 2 H₂O(l)