A particle of mass m is at rest at the origin at time $\mathrm{t} = 0$. It is subjected to a force $\mathrm{F}(\mathrm{t}) = \mathrm{F}_{0}\mathrm{e}^{-\mathrm{bt}}$ in the $x$ direction. Its speed $v(t)$ is depicted by which of the following curves?