The 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 power is:

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