An issue of the highest sensitivity, which required the greatest finesse and delicacy, was handled in the most slapdash manner.

Answer: Option C

Carefulness : making sure of avoiding potential danger, mishap, or harm; cautious.
Attention : notice taken of someone or something; the regarding of someone or something as interesting or important.
Tact : skill and sensitivity in dealing with others or with difficult issues.
Action : the fact or process of doing something, typically to achieve an aim.
Finesse : great subtlety and tact in handling or manipulating people or difficult situations.

Synonym of Finesse is Tact