The correct option is D Usual
The words 'unprecedented' refers to something that is never done or known before.
Option A, exceptional refers to something unusual or not typical.
Option B, consistent refers to something unchanging in nature, standard or effect over time.
Option C, abnormal refers to something deviating from what is normal or common.
Option D, usual refers to something that is habitually or typically occurring.
Thus, according to the meaning, the word 'usual' is the farthest in meaning from the word 'unprecedented'.