Ans : [B] When the thief keeps eluding the police, he is being elusive.
elusive - Difficult to find, catch or achieve.
allusive - Using or containing suggestion rather than explicit mention.
The correct alternatives for the incorrect answers are :
A. When the teacher alludes to different authors, he is being allusive.
C. Matters that are difficult to understand, identify or remember are elusive.
D. Mirages can be elusive, but a better way to express them is illusory.