He is very discreet while deciding such matters.

Answer: Option C

Obstinate : stubbornly refusing to change one's opinion or chosen course of action, despite attempts to persuade one to do so.
Cunning : having or showing skill in achieving one's ends by deceit or evasion.
Prudent : acting with or showing care and thought for the future.
Trustworthy : able to be relied on as honest or truthful.
Discreet : careful and prudent in one's speech or actions, especially in order to keep something confidential or to avoid embarrassment.

Synonym of Discreet is Prudent