Answer:
The shelf should be 0 degrees relative to the floor.
Explanation:
When an object is parallel to the floor, it means that it is aligned with the floor at the same angle and does not slope up or down.
In other words, the angle between the shelf and the floor is 0 degrees.
So, to attach the shelf so that it is parallel to the floor, Dana should ensure that the angle between the shelf and the floor is 0 degrees.