Commonly, adjectives of opposite meaning are formed by adding a prefix such as un, in, or dis.

A. clear – unclear, important – unimportant, predictable – unpredictable, believable – unbelievable, common – uncommon, aware – unaware, ambiguous – unambiguous, conventional – unconventional, certain – uncertain
B. definite – indefinite, correct – incorrect, comparable – incomparable, complete – incomplete, evitable – inevitable, expensive – inexpensive
C. able – disable, assemble – disassemble, content – discontent, similar – dissimilar