Particle $A$ moves along the $X$-axis with a uniform velocity of magnitude $10 \ m/s$. Particle $B$ moves with a uniform velocity of $20 \ m/s$ along a direction making an angle of $60^{\circ}$ with the positive direction of the $X$-axis as shown in the figure. The relative velocity of $B$ with respect to $A$ is

• A
  $10 \ m/s$ along the $X$-axis
• B
  $10 \sqrt{3} \ m/s$ along the $Y$-axis (perpendicular to the $X$-axis)
• C
  $10 \sqrt{5} \ m/s$ along the bisection of the velocities of $A$ and $B$
• D
  $30 \ m/s$ along the negative $X$-axis