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