Two identical lenses made of the same material of refractive index 1.5 have the focal length 12 cm. These lenses are kept in contact and immersed in a liquid of refractive index 1.35. The combination behaves as

A

convex lens of focal length 27 cm

B

concave lens of focal length 6 cm

C

convex lens of focal length 9 cm

D

convex lens of focal length 6 cm