In a radioactive material the activity at time `t_(1)` is `R_(1)` and at a later time `t_(2)`, it is `R_(2)`. If the decay constant of the material is `lambda`, then

Options

A. `R_(1)=R_(2)e^(lambda(t_(1)-t_(2))`
B. `R_(1)=R_(2)e^((t_(1)//t_(2))`
C. `R_(1)=R_(2)`
D. `R_(1)=R_(2)e^(-lambda(t_(1)-t_(2))`