[单选题]
The efficiency of a Carnot engine is op/sugq+d7 -h*8p9wdd 3f dmh35.0%. What is the temperatx7ewdyl*ejt j .o58 m5ure of the cold resej5.d 7wx8* lyo5eej tmrvoir if the temperature of the hot reservoir is $500 ^{\circ}K$?
A. $175 \; K$
B. $325 \; K$
C. $269 \; K$
D. $231 \; K$
