Silver : Ag :: Lead : ? Choose the option that completes the analogy.

The relation is an element : the short symbol chemists write for it, several of which are drawn from the old Latin names. Silver is Ag, from argentum; lead is Pb, from plumbum. Each distractor is the symbol of a different metal that keeps company with lead in the heavy corner of the table — Sn is tin, Au is gold and Hg is mercury.