The correct option is B relief
The word 'anxiety' refers to a feeling of worry and nervousness.
Option A, pleasure refers to a feeling of happy satisfaction a enjoyment.
Option B, happiness refers to the state of being happy.
Option C, relief refers to a feeling reassurance and relaxation.
Option D, laughter refers to the action and sound of laughing.
Thus, according to the meaning, the word 'relief' is the opposite of the word 'anxiety'.