还是陈向东里面的：

If C is the tmeperature in degrees Celsins and F is the temperature in degrees Fahrenheit, then the relationship between tmeperatures on the two scales is expressed by the equation 9C=5(F-32). On a day when the temperature exptremes 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?

A  65/9           B. 13         C. 25          D. 45            E. 81

CXD 的解释是：根据C=5/9(F-32)， 可得#C=5/9#F， 所以#C=5/9*45=25

（注：原书中#应为“三角or delta"，我因打不出delta符号，用#代替。）

highlight部分怎么出来的？32不要减掉了？

多谢！

delta C= C1- C2= 5/9*(F1-32) - 5/9*(F2-32)=5/9*(F1-F2)=5/9* delta F.

45 is the difference of F1-F2.