A mass attached to a spring is pulled to the right of its equilibrium position and released. The period of oscillation for this mass and spring is 20 seconds. Taking "to the right" to be positive, during which period of time is the velocity negative and increasing?

1. between 0 and 5 seconds
2. between 5 and 10 seconds
3. between 10 and 15 seconds
4. between 15 and 20 seconds