The correct option is B Boring
The word 'fascinating' refers to something extremely interesting.
Option A, interesting refers to something that arouses curiosity or interest.
Option B, boring refers to something not interesting or tedious.
Option C, enthusiastic refers to having or showing intense and eager enjoyment.
Option D, attractive refer to something pleasing or appealing to the senses.
Thus, according to the meaning, the word 'boring' is the antonym of the word 'fascinating'.