The frequency response of a linear, time-invariant system is given by $H(f)=\dfrac{5}{1+j 10 \pi f}$. The step response of the system is
- $5\left(1-e^{-5 t}\right) u(t)$
- $5\left(1-e^{-\frac{t}{5}}\right) u(t)$
- $\frac{1}{5}\left(1-e^{-5 t}\right) u(t)$
- $\frac{1}{5}\left(1-e^{-\frac{t}{5}}\right) u(t)$