If f(x) = |x| and g(x) = |x| − 4, which transformation is applied to f(x) to get g(x)?
A.a vertical transformation of f(x) four units upward
B.a horizontal transformation of f(x) four units to the left
C.a horizontal transformation of f(x) four units to the right
D.a vertical transformation of f(x) four units downward