求解：

英鸣

although the supreme court ruled as long age as 1880 that blacks could not be excluded outright from jury service, nearly a century of case-by case adjudication has been necessary to develp and enforce the principle that all juries must be drawn from a fair cross section of the community .  

A. has bee necessary to develop and enforce the principle that all juries must be
B. was necessary for developing and enforcing the principle of all juries being.
请问B为什么不对？如果不用being 这个错误词解释的话。

英鸣

谢谢mslancaster . ^_^

mslancaster

原文的情态动词不能随意去掉，因为会改变句子的逻辑意思和态度。

题目说了1880年开始，将近100年的case by case adjudication才导致了后面那个结果，因此是一个持续了100年的过程，用has been表示持续，而不用was表示发生在过去某一时间点。