Sentence Correction

Although the Supreme Court ruled as long ago as 1880 that Blacks could not be excluded outright from jury service, nearly a century of case-by-case adjudication has been necessary to develop and enforce the principle that all juries must be drawn from "a fair cross section of the community."
(A) has been 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
(C) was to be necessary in developing and enforcing the principle of all juries to be
(D) is necessary to develop and enforce the principle that all juries must be
(E) will be necessary for developing and enforcing the principle of all juries being

To me it looks, A. What is the OA?

Thanks
Mankey