Equation of motion in the same direction are given by 
    ${\mathrm{y}}_1=2\mathrm{asin}(\mathrm{\omega t}-\mathrm{kx})$ and ${\mathrm{y}}_2=2\mathrm{asin}(\mathrm{\omega t}-\mathrm{kx}-\mathrm{\theta })$
The amplitude of the medium particle will be 

• A

  $2\mathrm{acos\theta }$

• B

  $\sqrt{2}\mathrm{acos\theta }$

• C

  $4\mathrm{acos\theta }/2$

• D

  $\sqrt{2}\mathrm{acos\theta }/2$