If `f (x) + g(x) = e^(–x)` where `f (x)` is an even function and `g(x)` is an odd function, then `f (x)` and `g(x)` must be

Options

A. `f(x)=(e^-x+e^x)/2,` `g(x)=(e^-x-e^x)/2,`
B. `f(x)=(e^-x+e^(2x))/2,` `g(x)=(e^-x-(e^(2x)))/2,`
C. f(x)=constant, `g(x)=3x`
D. none of these