Which function is the inverse of f(x)=50,000(0.8)^x?

Af^-1(x)=log0.8(x/20,000)

Bf^-1(x)=log50,000(x/0.8)

Cf^-1(x)=log0.8(50,000/x)

Df^-1(x)=log0.8(x/50,000)

P.S. There's more points if you answer this same question. I posted it three days ago.