The Granger Cases of the 1870s

(a) sealed the fate of the U.S. railroad system, even though the cases were covered under a case involving a grain elevator.
(b) came before the U.S. Supreme Court because state legislatures had passed laws in the 1870s to allow state agencies to control various aspects of railroad operation, including rate setting; these laws were then challenged by railroad companies.
(c) established the principle that railroads were unquestionably subject to permanent regulation.
(d) are true for all of the above.

(d)