Two particles move parallel to the \[x\]-axis about the origin with same amplitude '\[a\]' and frequency\[\omega \]. At a certain instant they are found at a distance \[a/3\] from the origin on opposite sides but their velocities are in the same direction. What is the phase difference between the two?

• A. \[{{\cos }^{-1}}\frac{7}{9}\]  
• B. \[{{\cos }^{-1}}\frac{5}{9}\]
• C. \[{{\cos }^{-1}}\frac{4}{9}\]  
• D. \[{{\cos }^{-1}}\frac{1}{9}\]