单选题
If C is the temperature in degrees Celsius and F is the temperature in degrees Fahrenheit，then the relationship between temperatures on the two scales is expressed by the equation 9C=5(F-32)．On a day when the temperature extremes recorded at a certain weather station differed by 45 degrees on the Fahrenheit scale，by how many degrees did the temperature extremes differ on the Celsius scale?
【正确答案】
C
【答案解析】Let F represent the larger extreme on the Fahrenheit scale. Then, F- 45 is the smaller extreme. It follows that the difference in the temperatures on the Celsius scale is