You are given a functionf(x) and told that the function g(x)=a^f(x), a>0, has a slope equal to 2lna at x=0. Which of the following functions could be f(x).

a) f(x)=x^2

b)f(x)=e^x-1

c) f(x)=2x^2+4x

d)f(x)=2cos(x)-2

e) f(x)=2ln(x+1)