The activity of a sample of radioactive material `A_(1)` at time `t_(1)` and `A_(2)` at time `t_(2)(t_(2)gtt_(1))`. Its mean life is `T`.
A. `A_(1)t_(1)=A_(2)t_(2)`
B. `(A_(1)-A_(2))/(t_(2)-t_(1))="constant"`
C. `A_(2)=A_(1)e^((t_(1)-t_(2)//T))`
D. `A_(2)=A_(1)e^((t_(2)//Tt_(2)))`
