Which of the following functions satisfies f′(x)=f(x)f'(x) = f(x)f′(x)=f(x)?
f(x)=exf(x) = e^xf(x)=ex
f(x)=xef(x) = x^ef(x)=xe
f(x)=sinxf(x) = \sin xf(x)=sinx
f(x)=0f(x) = 0f(x)=0