Activities of three radioactive substances A,B and C are represented by the curves  A,B and C in the figure . Then their half lives ${\text{T}}_{\frac{\text{1}}{\text{2}}}\left(\text{A}\right){\text{:T}}_{\frac{\text{1}}{\text{2}}}\left(\text{B}\right){\text{:T}}_{\frac{\text{1}}{\text{2}}}\left(\text{C}\right)\text{: }$ are in the ratio :

• A

  2 : 1  : 3

• B

  4 : 3  : 1

• C

  3 : 2  : 1

• D

  2 : 1  : 1