Which equation listed below would produce this activation function?

Activation function

$($:$x$:$)=$max$(0,x)$

$($:$x$:$)=x$

$($:$x$:$)=\frac{\text{e}\text{x}\text{p}()}{{\displaystyle \underset{j}{\overset{?}{}}}\text{e}\text{x}\text{p}(x_i)}$

$($:$x$:$)=\frac{1}{1+e^{-x}}$

None of the above are the correct activation function for this graph.