If wire rope guard rails are used what must also be done?

A Deceleration device.
A rope, wire rope, or strap with connectors at each end for connecting the 5 point body harness to a lifeline, or anchorage.

Look under OSHA Flashcards on Quizlet and..
OSHA: Fall Protection in Construction, Subpart M and just past that area in the document.

This is from that document on page 13 and 14:  
Fall Restraint Systems:  While fall restraint systems are not mentioned in Subpart M, OSHA recognizes a fall restraint system as a means of prevention. The system, if properly used, tethers a worker in a manner that will not allow a fall of any distance. This system is comprised of a body belt or body harness, an anchorage, connectors, and other necessary equipment. Other components typically include Photo: Skip Pennington OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION 1 4 a lanyard, a lifeline, and other devices. For a restraint system to work, the anchorage must be strong enough to prevent the worker from moving past the point where the system is fully extended, including an appropriate safety factor. *In a November 2, 1995 interpretation letter to Mr. Dennis Gilmore, OSHA suggested that, at a minimum, a fall restraint system must have the capacity to withstand at least 3,000 pounds or twice the maximum expected force that is needed to restrain the person from exposure to the fall hazard. In determining this force, consideration should be given to site-specific factors such as the force generated by a person (including his/her tools, equipment, and materials) walking, slipping, tripping, leaning, or sliding along the work surface.

Ithink the answer is letter d