Question

what does the horizontal line on a distance - time graph represent? the object is moving at a constant speed. the object is not moving. the object is slowing down. the object is speeding up.

Explanation:

On a distance - time graph, the slope represents speed. A horizontal line has a slope of 0. Speed is calculated as the change in distance over the change in time ($v=\frac{\Delta d}{\Delta t}$). When the slope is 0, $\Delta d = 0$ for any $\Delta t$, meaning the distance does not change with time, so the object is not moving.

Answer:

The object is not moving.