Which one of the following statements about polynomials is always true?
(a) If f(a)=0, then (x+a) is a factor of f(x).
(b) If (x−a) is a factor of f(x), the remainder when f(x) is divided by (x−a) is a.},{
(c) If f(a)=0, then (x−a) is a factor of f(x).
(d) If (x−a) is a factor of f(x), then f(−a)=0.