The activity of a sample of a radioactive material is A, at time \[{{t}_{1}}\] and \[{{A}_{2}}\] at time \[{{t}_{2}}\] \[({{t}_{2}}>{{t}_{1}}).\] If its mean life T, then [BHU 2002]

• A.            \[{{A}_{1}}{{t}_{1}}={{A}_{2}}{{t}_{2}}\]                      
• B.            \[{{A}_{1}}-{{A}_{2}}={{t}_{2}}-{{t}_{1}}\]
• C.            \[{{A}_{2}}={{A}_{1}}{{e}^{({{t}_{1}}-{{t}_{2}})/T}}\]            
• D.            \[{{A}_{2}}={{A}_{1}}{{e}^{({{t}_{1}}/{{t}_{2}})T}}\]