#### Answer

Choice C

#### Work Step by Step

Using the Quotient Rule of radicals which is given by $\sqrt[n]{\dfrac{x}{y}}=\dfrac{\sqrt[n]{x}}{\sqrt[n]{y}}{},$ the expression, $
\dfrac{\sqrt{5a^4}}{\sqrt{5a^3}}
,$ is equivalent to
\begin{array}{l}\require{cancel}
\dfrac{\sqrt{5a^4}}{\sqrt{5a^3}}
\\\\=
\sqrt{\dfrac{5a^4}{5a^3}}
\\\\=
\sqrt{\dfrac{\cancel5a^{4-3}}{\cancel5}}
\\\\=
\sqrt{a}
.\end{array}
Hence, $\text{
Choice C
.}$