Average speed for the trip south was 20 miles/hour.
In this statement average speed with direction is given which can be referred to as "Velocity"
Correct option : D) Velocity
[tex]\text{ Velocity}=\frac{\text{Displacement}}{\text{Time}}[/tex]
Thus, correct option will be D.
Find more information about Velocity here:
brainly.com/question/4931057