Prove :If $u(x)\in \displaystyle{H^{l}(R)}$, then $u(x)\in \displaystyle C^{l-1}(R)$

I come across this problem in my functional analysis book.Prove:

If $u(x)\in \displaystyle{H^{l}(R)}$, then

$u(x)\in \displaystyle C^{l-1}(R)$,$\displaystyle\lim_{x\to|\infty|}D^{\alpha}u=0 ,\alpha=0,1,...l$

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