$(5\mathrm{.}1)$ The Laplace transform of $e^{-t}$ is

$\frac{1}{(s-1{)}^2}$

$\frac{1}{s^2-1}$

$\frac{1}{s-1}$

$\frac{1}{s+1}$

$\frac{1}{(s+1{)}^2}$

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