What Does the Proportionality Principle Require

What does the proportionality principle require?

A) It requires that, before employing biochemical weapons, we weigh the relative advantages of conventional weapons as a viable alternative.
B) It requires that, before engaging in war or the use of force, we consider the likely costs and benefits of doing so, as opposed to choosing alternative courses of action (or no action) .
C) It requires that, before considering non-violence, we consider the likelihood of international repercussions.
D) It requires that, before we call a war "just" we commence a values-assessment and consult political and religious leaders.