The correct option is C abundance
The word 'dearth' refers to a scarcity of lack of something.
Option A, extravagance refers to excessive elaboration.
Option B, scarcity refers to shortage.
Option C, abundance refers to a very large quantity of something.
Option D, sufficiency refers to the condition or quality of being adequate or sufficient.
Thus, according to the meaning, the word 'abundance' is the opposite of the word 'dearth'.