The Landmark NIOSH Studies on Back Belts Have Shown No

The landmark NIOSH studies on back belts have shown no significant difference in the incidence of workers' compensation claims:

A) between workers who are required to wear back belts and those who are not required to do so.
B) between workers who wear back belts everyday vs.those who never wear them or,if they do wear them,do so only occasionally.
C) both of the above.
D) none of the above.