Read the following article and answer the question by choosing from the options.

Kerri tied in and made her way to the top of the cliff in short order while I belayed her . ( Belaying someone basically means you 're taking up the slack in the rope as they climb using a belaying device so they do n't fall too far if they lose contact with the rock and lowering them when they ' ve finished climbing . ) I went next and followed a slightly different route at the bottom that avoided a small oak tree that was growing in a slightly inconvenient location . Eventually the route I was following converged with the route Kerri followed and I made it to the top .

What may be the reason for belaying ?
Available options:
[A]. To provide security for the person climbing .;
[B]. To make sure that they have the right footing .;
[C]. To ensure that the person thinks they will fall .;
[D]. None of the above choices .;...A:
[A].