Monochromatic light of wavelength $\lambda = 4770 \ \mathring{A}$ is incident separately on the surface of four different metals $A, B, C$ and $D$. The work functions of $A, B, C$ and $D$ are $4.2 \ \text{eV}, 3.7 \ \text{eV}, 3.2 \ \text{eV}$ and $2.3 \ \text{eV}$, respectively. From which of these metals will electrons be emitted?

• A
  $A, B, C$ and $D$
• B
  $B, C$ and $D$
• C
  $C$ and $D$
• D
  $D$ only