The reaction $$xX(g) \rightleftharpoons yY(g) + zZ(g)$$ was carried out at a certain temperature with an initial pressure of X of 30 bar. Initially Y and Z were not present. If the equilibrium partial pressures of X, Y and Z are 20, 5 and 10 bar respectively, $$x \colon y \colon z$$ is

A

$$4 \colon 1 \colon 2$$

B

$$2 \colon 1 \colon 2$$

C

$$1 \colon 2 \colon 1$$

D

$$1 \colon 1 \colon 2$$