Which of the following statement correctly defines the not(X) rule?

Which of the following statement correctly defines the not(X) rule?

Which of the following statement correctly defines the not(X) rule?       

Answers:      

A.
not(X) :- !, X, fail.
not(_).
   
B.
not(X) :- X, fail, !.
not(_).
     
C.
not(X) :- X, !, fail.
not(_).
     
D.
not(_).

Answer. C.