OG 34

In comparing the United States government's definition of services with the classical definition,the author suggests that the classical definition is

a) more pragmatic
b) more difficult to apply
c) less ambiguous
d) more widely used
e) more arbitrary

为何c错呢.我觉得文中明确指出U.S.gov的definition就是such ambiguity (line 25).
但我看了答案后觉得b也的确是有道理的. 请问这道题目的解题原则是什么呢. 谢谢!

中明确指出U.S.gov的definition就是such ambiguity (line 25).

但没在这点上就两者进行比较