The value of x so that \[{{\left( \frac{2}{7} \right)}^{4}}.{{\left( \frac{2}{7} \right)}^{3}}={{\left( \frac{2}{7} \right)}^{4x-1}}\] is

• A.  1                                
• B.  2   
• C.  3                                
• D.  4