SOLUTION
To solve this, let's first simplify, we have
[tex]\begin{gathered} \sqrt{4x^2}\times\sqrt{20x^2} \\ 2x\times\sqrt{20}\times x \\ 2x^2\times\sqrt{4\times5} \\ 2x^2\times2\times\sqrt{5} \\ 4x^2\times\sqrt{5} \\ =4x^2\sqrt{5} \end{gathered}[/tex]
Hence the answer is option C
