During the 'released position', which of the following is true?

In the context of hydraulic brake systems, the 'released position' refers to the state of the brake system when the brakes are not being applied. During this phase, the ports between the reservoir and the hydraulic circuits are indeed open, allowing hydraulic fluid to flow freely back into the reservoir. This is crucial because it enables the brake system to reset itself and ensures that the return of hydraulic pressure does not occur until the brake pedal is pressed again.

In contrast, the other options do not accurately describe the state of a hydraulic brake system during the 'released position.' For instance, if the hydraulic circuits were closed, it would indicate that pressure is maintained, which is not the case when brakes are released. Similarly, pressure is not built up in this position; instead, it is at its lowest point because the brake calipers are disengaged, preventing any clamping force on the brake pads.