The value of \(\mathop {\lim }\limits_{x \to a} \frac{{\sqrt {a + 2x} - \sqrt {3x} }}{{\sqrt {3a + x} - 2\sqrt x }}\) is

• A. \(\frac 2 3\)
• B. \(\frac 2 {\sqrt 3}\)
• C. \(\frac {3\sqrt 3} 2\)
• D. \(\frac 2 {3\sqrt 3}\)