$A$ metal surface is illuminated by light of two different wavelengths $248 \ nm$ and $310 \ nm$. The maximum speeds of the photoelectrons corresponding to these wavelengths are $u_1$ and $u_2$ respectively. If the ratio $u_1 : u_2 = 2 : 1$ and $hc = 1240 \ eV \ nm$,the work function of the metal is nearly $:-$ (in $eV$)

• A
  $3.7$
• B
  $3.2$
• C
  $2.8$
• D
  $2.5$