In a voltaic cell, the spontaneous reaction that occurs is 2 Ag$^+$ + Cu (s) ? Cu$^{2+}$ + 2 Ag (s). Which of the following statements are true?
I. The silver metal is the cathode.
II. A salt bridge is unnecessary in this voltaic cell.
III. Copper (s) is reduced.
I only
all of these
I and III only
III only
II and III only