The thermal efficiency of Gas turbine plant is

A

$$r^{\gamma -1}$$

B

$$1 - r^{\gamma -1}$$

C

$$1 - \left(\frac{1}{r}\right)^{\frac{\gamma}{(\gamma-1)}}$$

D

$$1 - \left(\frac{1}{r}\right)^{\frac{\gamma-1}{\gamma}}$$