The composition of aqua-regia is

• A
  $\text{Dil. HCl} : \text{Conc. HNO}_3 = 3:1$
• B
  $\text{Conc. HCl} : \text{Dil. HNO}_3 = 3:1$
• C
  $\text{Dil. HCl} : \text{Dil. HNO}_3 = 3:1$
• D
  $\text{Conc. HCl} : \text{Conc. HNO}_3 = 3:1$