Just like fingerprints, each person’s DNA is ________unless he has a twin．

It’s hard for the young people to imagine what _____ conditions their parents once lived under.

—What do you plan to do on the ___________ May Day holiday?—I have no idea. Probably, I will spend it by doing many papers.

People complain that decisions to approve or deny a permit are often ____ rather than based on fixed criteria.

    -- I have warned him of the danger but he insisted on going there alone. -- What a _______ boy!