If $\vec F$ is the force acting on a particle having position vector $\vec r$ and $\vec \tau$ is the torque of this force about the origin,then:

• A
  $\vec r \cdot \vec \tau = 0$ and $\vec F \cdot \vec \tau \neq 0$
• B
  $\vec r \cdot \vec \tau \neq 0$ and $\vec F \cdot \vec \tau = 0$
• C
  $\vec r \cdot \vec \tau > 0$ and $\vec F \cdot \vec \tau < 0$
• D
  $\vec r \cdot \vec \tau = 0$ and $\vec F \cdot \vec \tau = 0$