Which of the following is true?
A.
(A) If for all , then 0 is a critical point and a local minimum point of f(x) .
B.
(B) If a,b are the only two local minimum points of f, then for all .
C.
(C) If , , then is a critical point and a local maximum point of f(x)
D.
(D) None of above is true.