Two particles are executing simple harmonic motion at an instant of time 't' their displacements are  ${\text{y}}_{\text{1}}\text{=acos(wt)}$ and ${\text{y}}_2\text{=asin(wt)}$ . Then the phase difference between ${\text{y}}_{\text{1}}$  and ${\text{y}}_{\text{2}}$  is

• A

  ${120}^{\circ }$

• B

  ${90}^{\circ }$

• C

  ${180}^{\circ }$

• D

  Zero