Explanation
Let's look at the meanings of the given word and marked option:
Rude- offensively impolite or ill-mannered
Polite- having or showing behavior that is r espectful and considerate of other people
Let's look at the meanings of the other given options:
Sweet- having the pleasant taste characteristic of sugar or honey; not salty, sour, or bitter
Decent- conforming with generally accepted standards of respectable or moral behavior
Gentle- having or showing a mild, kind, or tender temperament or character
Hence from the given meanings, we find that Rude and Polite are antonyms.
