In an experiment on the photoelectric effect,the wavelength of the incident radiation is $\lambda$. The wavelength of the incident radiation is reduced to $\frac{1}{3}$ of the initial value,and the maximum kinetic energy of the photoelectron is observed to be $n$ times the previous value. The threshold wavelength for the metal plate is:

• A
  $\left( \frac{n - 1}{n - 3} \right) \lambda$
• B
  $\left( \frac{n}{n - 3} \right) \lambda$
• C
  $\frac{(n + 1) \lambda}{n - 3}$
• D
  $\frac{3 \lambda}{n}$