The correct option is A work
The word 'recreation' refers to the activity done for enjoyment when one is not working.
Option A, work refers to the things to be done.
Option B, boredom refers to the state of feeling bored.
Option C, leisure refers to free time.
Option D, diversion refers to the action of turning something aside form its course.
Thus, according to the meaning, the word 'work' is the opposite of the word 'recreation'.