The correct option is B deterrent
Deterrent means a thing that discourages or is intended to discourage someone from doing something. Iraq's chemical warfare discourages even superpowers. Hence, Option B is correct. Among the rest of the options, pretext means a reason given in justification of a course of action that is not the real reason, constraint means a limitation or restriction, detriment means the state of being harmed or damaged, precaution means a measure taken in advance to prevent something dangerous, unpleasant, or inconvenient from happening. These options do not express the intended meaning, hence incorrect.