Two identical solid blocks A and B are made of two different materials. Block A floats in a liquid with half of its volume submerged. When block B is pasted over A, the combination is found to just float in the liquid. The ratio of the densities of the liquid, material of A and material of B is given by

A

$$1 \colon 2 \colon 3$$

B

$$2 \colon 1 \colon 4$$

C

$$2 \colon 1 \colon 3$$

D

$$1 \colon 3 \colon 2$$