The function g(x) = 2^x. the function f(x) = 2^x+k and k< 0. which of the following statements is true.
A The graph of f(x) is shifted k units to the left of the graph g(x)
B The graph of f(x) is shifted k units to the right of the graph g(x)
C The graph of f(x) is shifted k units above the graph of g(x)
D The graph of f(x) is shifted k units below the graph of g(x)