The slope of the line on a distance-time graph is a. distance b. time c. speed d. displacement

If the graph shows the plot of distance as a function of time, then
the slope of the graph is (change in distance) / (time for the change).

That's speed. (C)

If there was no gravity then their would be no downword force on the football to have it return the the grownd, and if there was no friction (mainly air friction) then there would be no opposing force the stop the ball from moving through the air allowing the ball to travle ∞.