A. Exposed
B. Revealed
C. Concealed
D. Contended
Discovered : find unexpectedly or during a search.
Exposed : make (something) visible by uncovering it.
Revealed : make (previously unknown or secret information) known to others.
Concealed : kept secret, hidden
Contended : struggle to surmount (a difficulty).
Thus, antonym of Discovered is Concealed
