A heat engine performs the reversible cycle abca with 9.0 moles of an ideal gas, as shown in the figure. Path ca is an adiabatic process. The temperatures at points a and b are 300 K and 500 K, respectively. The volume at point c is 0.20 m3 . The adiabatic constant of the gas is 1.60. The thermal efficiency of this engine is closest to:
A) 0.070
B) 0.10
C) 0.13
D) 0.16
E) 0.19