The General Manager is quite tactful and handles the workers union very effectively.

Answer: Option C

Tactful : having or showing skill and sensitivity in dealing with others or with difficult issues.
Relaxed : free from tension and anxiety.
Strict : demanding that rules concerning behaviour are obeyed and observed.
Naive : (of a person or action) showing a lack of experience, wisdom, or judgement.
Disciplined : showing a controlled form of behaviour or way of working.

Antonym of Tactful is Naive