Gold numbers of protective colloids $A, B, C$ and $D$ are $0.50, 0.01, 0.10$ and $0.005$,respectively. The correct order of their protective powers is

• A
  $A < C < B < D$
• B
  $C < B < D < A$
• C
  $A < C < B < D$
• D
  $D < B < C < A$