Photoelectric emission is observed from a metal surface with incident frequencies `v_(1) and v_(2)` where `v_(1) gt v_(2)`. If the kinetic energies of the photoelectrons emitted in the two cases are in the ratio `2 : 1`, then the threshold frequency `v_(0)` of the metal is

A. `v_(1) = v_(2)`

B. `(v_(1) - v_(2))/(h)`

C. `2 v_(1) - v_(2)`

D. `2v_(2) - v_(1)`