A radioactive nuclide is produced at the constant rate of n per second (say, by bombarding a target with neutrons). The expected number `N` of nuclei in existence `t` s after the number is `N_(0)` is given by
A. `N=N_(0)e^(-lambdat)`
B. `N=n/lambda+N_(0)e^(-lambdat)`
C. `N=n/lambda+(N_(0)-n/lambda)e^(-lambdat)`
D. `N=n/lambda+(N_(0)+n/lambda)e^(-lambdat)`