P(a, a, a) is a point in space. Three forces each of magnitude F are acting at P in the positive X-direction, positive Y-direction and positive Z-direction. The magnitude of the torque due to the system of forces about the origin is

• A

  3Fa

• B

  zero

• C

  $\sqrt{3}Fa$

• D

  $\frac{Fa}{\sqrt{3}}$