The correct option is D Efficiency
The exact meaning of the word 'efficacy' is to have an ability to produce intended results, which closely relates to the word 'efficiency'. The word 'efficiency' means to complete a given task with expected results. While 'delicacy' means something that's tasty; 'Ruthlessness' means not being able to show pity towards others and 'Solemnity' means being sincere about a commitment you've made.