But some causes are more controversial than others. Which choice below best manifests a genuinely just cause under ius ad bellum?

The correct answer to this open question is the following.

You forgot to include the choices of the questions. Without the choices, we do not have references. However, hope we can help with the following comments.

Jus ad bellum is the kind of legislation that authorizes the transition from a state of peace and agreement to a state of war, where the use of the armed forces is justified. It implies that just a legitimate authority can wage war when no other option is left. Just ad bellum have some principles, that include: right authority, right intention, proportionality, reasonable hope, and last intention, which can be understood as the case in which war is the last resource after a long period of diplomacy and negotiation, under the right authority and the valid reasons to proceed as the last resource to solve an issue.