Effective october 25, 1976 osha’s standard code 29 cfr 1928.51, forced a change in tractors. what change was made to protect farm workers? manufactured after what date? a. all tractors must be equipped with rollover protective structures b. all tractors used by farm employees must be equipped with rollover protective structures c. all tractors must adhere to visibility standards d. all tractor operators must adhere to public highway rules