The volume of an ideal gas $$(\gamma = 1.5)$$ is changed adiabatically from 5 litres to 4 litres. The ratio of initial pressure to final pressure is:

A

$$\frac{16}{25}$$

B

$$\frac{4}{5}$$

C

$$\frac{8}{5\sqrt{5}}$$

D

$$\frac{2}{\sqrt{5}}$$