Which of the following methods can increase friction when repelling?

Employing a redirect effectively increases friction during repelling by altering the direction of the rope and the angle at which it interacts with the anchor points. This adjustment creates additional points of contact and can lead to increased friction, helping to control the descent more efficiently. Redirection allows the rope to pass through the anchor at a different angle, which can further enhance the resistance against the pull of gravity. This technique is particularly useful when the terrain is steep or if the descent line is straightforward, as it reduces the risk of sliding too quickly.

In contrast, utilizing a single carabiner tends to create a more direct and potentially frictionless path along the rope, which may not contribute to increased resistance. Choosing lightweight ropes could reduce the overall handling of the descent but does not inherently increase friction. Rappelling with straight drops, while straightforward, often lacks the additional friction generated by redirections, making it less effective for controlling speed. Thus, using a redirect stands out as the method most conducive to increasing friction during repelling.