Under the Occupiers' Liability Act 1957, When Will a Warning

Under the Occupiers' Liability Act 1957, when will a warning be sufficient to discharge an occupier's duty to a particular visitor?

A) Where an occupier has, in relation to the relevant circumstances, restricted, excluded, or otherwise modified their duty to the visitor.
B) Where, in all the circumstances, it is enough to ensure that the premises are reasonably safe
C) Where, in all the circumstances, it is enough to ensure that the visitor is reasonably safe
D) Where, in all the circumstances, the occupier has taken reasonable steps to bring the danger to the visitor's attention