Equation of a progressive wave is given by \[y=0.2\cos \pi \left( 0.04t+.02x-\frac{\pi }{6} \right)\] The distance is expressed in cm and time in second. What will be the minimum distance between two particles having the phase difference of \[\pi /2\]

• A.            4 cm                                         
• B.            8 cm
• C.            25 cm                                      
• D.            12.5 cm