a vertical one
It is false
Yes it is.
You can show the motion of an object on a line graph in which you plot distance versus time.
The slope of a distance versus time graph provides the instantaneous speed of an object. If data from this graph is then used to construct a speed versus time graph, the slope of that graph would provide the instantaneous acceleration.
if the speed is zero then the distance versus time line will be horizontal
the slope show the velocity of the object which show its direction and magnitude.
Note that the graph can't show velocity, only speed. The slope of the graph is the magnitude of acceleration. The area under the graph is distance covered.
The slope of the line would decrease.
If the line formed by the graph is straight, the speed is constant. A horizontal line would show the object as stationary.
It shows acceleration.