Choice "A" is correct. OSHA allows inspections at the request of employees. 29 U.S.C. §657(f)(1)
Choice "c" is incorrect. OSHA provides for searches without a warrant based on probable cause. 29 U.S.C. §657(a)
Choice "d" is incorrect. OSHA provides for searches during regular business hours or at other reasonable times. 29 U.S.C. §657(a)
Choice "b" is incorrect. There is no 24-hour notice requirement.