The correct answer is A. Rafters.
Rafters are the main structural members of a roof that support the roof covering. They are typically made of wood or steel and are installed at an angle to the ground. The rafters are supported by the walls of the building or by a ridge beam. The roof covering is then attached to the rafters.
Purlins are horizontal members that support the rafters. They are typically made of wood or steel and are installed parallel to the rafters. The purlins are supported by the walls of the building or by a ridge beam.
Battens are small, horizontal members that are installed perpendicular to the rafters. They are typically made of wood or metal and are used to support the roof covering.
Struts are vertical members that are used to support other structural members. They are typically made of wood or steel and are installed between two other members.
In conclusion, the members which support covering material of a sloping roof are rafters.