Answer
Choice D.
Work Step by Step
Don’t use Celsius degrees or you will get the wrong efficiency of 50 percent.
Convert the temperature to kelvin, and use equation 15–5 to compute the upper limit on the efficiency of about 34 percent.
$$1-\frac{T_{low}}{T_{high}} = 1-\frac{573 K}{873 K} = 0.34$$
