Multiply and Then, If Possible, Simplify by Factoring $\sqrt{5 x} \sqrt{35 x}$

Multiple Choice

Multiply and then, if possible, simplify by factoring.
- $\sqrt{5 x} \sqrt{35 x}$

A) $5 x \sqrt{7}$
B) $25 x \sqrt{7}$
C) $5 \sqrt{7 x}$
D) $\sqrt{175 x^{2}}$