A Heat Engine Takes 2

A heat engine takes 2.0 moles of an ideal gas through the reversible cycle abca, on the pV diagram shown in the figure. The path bc is an isothermal process. The temperature at c is 820 K, and the volumes at a and c are 0.010 m³ and 0.16 m³, respectively. The molar heat capacity at constant volume, of the gas, is 37 J/mol·K, and the ideal gas constant is R = 8.314 J/(mol∙K) . The thermal efficiency of the engine is closest to

A) 0.26.
B) 0.026.
C) 0.33.
D) 0.40.
E) 0.53.