5 mL each of concentrated HCl, HNO3 and a mixture of concentrated

5 mL each of concentrated HCl, HNO3 and a mixture of concentrated HCl (15 mL) and concentrated HNO3 (5 mL) were taken in test tubes labelled as

A, B and C. A small piece of metal was put in each test tube. No change occurred in test tubes A and B but the metal got dissolved in test tube C. The

metal could be

(a) Al

(b) Au

(c) Cu

(d) Ag