The correct option is C prudent
“Discreet” means to be careful and prudent in one's speech or actions, especially in order to keep something confidential.
Option C is the correct answer because “prudent” means to be very careful, hence it is the correct meaning of the given word.
Option A is incorrect because “obstinate” means to stubbornly refuse to change one’s opinion, which is not relevant to the given word.
Option B is incorrect because “cunning” means having or showing skill in achieving one's ends by deceit or evasion, hence it is incorrect.
Option D is incorrect because “trustworthy” means able to be relied on as honest or truthful, which is incorrect as it is not relevant to the given word.