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A solution for the differential equation
$\qquad \dot{x}(t)+2 x(t)=\delta(t)$
with initial condition $x(0-)=0$ is

1. $e^{-2 t} \; u(t)$
2. $e^{2 t} \; u(t)$
3. $e^{-t} \; u(t)$
4. $e^{t} \; u(t)$