STOLIDITY

Stolidity means to be unmoved or resolute (in a negative sense) without listening to the arguments.
Posterity means 'for the future'. 
Proximity is a term used to describe how near a place is with reference to something. 
Agility is a term used to describe the ability to move quickly. 
Sobriety is a term used to describe the state of being sober or to process thing rationally. 

Sobriety is opposite in meaning to stolidity. Therefore, option D is the right answer.