What does $925$ sterling silver mean in terms of its alloy composition?

• A
  $7.5\% Ag$ and $92.5\% Cu$
• B
  $92.5\% Ag$ and $7.5\% Cu$
• C
  $9.25\% Cu$ and $90.75\% Ag$
• D
  $9.25\% Ag$ and $90.75\% Cu$