What Is Undergoing Oxidation in the Redox Reaction Represented by the Following

What is undergoing oxidation in the redox reaction represented by the following cell notation?
$\quad$$\quad$$\quad$ Pb(s) | Pb²⁺(aq) $\|$ H⁺(aq) | H₂(g) | Pt(s)

A) H₂(g)
B) H⁺(aq)
C) Pb²⁺(aq)
D) Pb(s)
E) Pt(s)