$A$ wooden cube (density of wood $d$) of side $l$ floats in a liquid of density $\rho$ with its upper and lower surfaces horizontal. If the cube is pushed slightly down and released,it performs simple harmonic motion of period $T$. Then,$T$ is equal to

• A
  $2\pi \sqrt {\frac{{l\rho }}{{\left( {\rho - d} \right)g}}} $
• B
  $2\pi \sqrt {\frac{{ld }}{{\rho g}}} $
• C
  $2\pi \sqrt {\frac{{l\rho }}{{dg}}} $
• D
  $2\pi \sqrt {\frac{{ld}}{{\left( {\rho - d} \right)g}}} $