A double convex lens of focal length 20 cm is made of glass of refractive index $\frac{3}{2}$. When placed completely in water $\left({ }_{\mathrm{a}}{\mathrm{\mu }}_{\mathrm{w}}=\frac{4}{3}\right)$, its focal length will be

• A

  80 cm

• B

  15 cm

• C

  17.7 cm

• D

  22.5 cm