#### Answer

Choice D

#### Work Step by Step

Simplifying the expression, $
\dfrac{\sqrt{4}}{\sqrt{16}}
$ (Choice D), results to
\begin{align*}
&
\dfrac{2}{4}
\\\\&=
\dfrac{1}{2}
.\end{align*}
Since $\dfrac{1}{2}\ne\sqrt{\dfrac{1}{2}}$, then the expression that is not equal to $\sqrt{\dfrac{1}{2}}$ is Choice D.