Add a prefix to make a word of opposite meaning for the words legible climax, agreement. 

Option A is correct because the prefixes 'il-', 'anti-', and 'dis-' can be used to form the opposite of 'legible', 'climax', and 'agreement', respectively. This results in 'illegible' (not clear enough to read), 'anticlimax' (a disappointing end to an exciting series of events), and 'disagreement' (lack of consensus).