Why Can It Be Hard to Achieve Credibility in International

Why can it be hard to achieve credibility in international bargaining?

A) There are no objective measures of power.
B) Leaders are irrational when they are bargaining.
C) States have an incentive to misrepresent their position to achieve a better bargain.
D) States never want to feign weakness.
E) Bargaining is best left to diplomats,but diplomats rarely know the full extent of their own state's power.