When no current is passed through a conductor.

When there is no current passing through a conductor then there is no charge will flow through conductor. So net charge will be zero. Because of no net charge all the electrons will be in a random motion. Due to random motion there is no net charge transfer. So the average velocity of a free electron over a large time period will be zero. If we see the average velocities of a free electrons it will also zero at an instant because of absence of net charge.

Conclusion : When no current is passed through a conductor. The average velocity of a free electron over a large period of time is zero and the average of the velocities of all the free electrons at an instant is zero. Option C and D are correct.