An air-standard Diesel cycle consists of the following process:
1-2: Air is compressed isentropically
2-3: Heat is added at constant pressure.
3-4: Air expands isentropically to the original volume
4-5: Heat is rejected at constant volume
If g and T denote the specific heat ratio and temperature, respectively, the efficiency of the cycle is
(a) $I-\frac{T_{4}-T_{1}}{T_{3}-T_{2}}$ 
(b) $I-\frac{T_{4}-T_{1}}{\gamma \left ( T_{3}-T_{2} \right )}$
(c) $I-\frac{\gamma \left ( T_{4}-T_{1} \right )}{ \left ( T_{3}-T_{2} \right )}$ 
(d) $I-\frac{ \left ( T_{4}-T_{1} \right )}{\left ( \gamma -1 \right ) \left ( T_{3}-T_{2} \right )}$ 