In this problem, we are trying to understand which of the possible options is the dependent variable when a car is traveling at a set speed of 60 miles per hour.
Let's consider each of the options:
A. The speed at which the car travels - Given in the problem statement that this is constant i.e., 60 miles per hour. So, it does not depend on any other variables and hence it is an independent variable.
B. The age of the car - This variable is also not dependent on the speed at which the car is moving or the time, therefore it is also independent.
C. The number of hours the car has traveled - This is an independent variable because its changes in time would not be influenced by any other factor in this context.
D. The distance the car has traveled - This variable depends on the time the car has been traveling. The longer the vehicle has been in motion, the farther it has gone. Hence it is a dependent variable.
So, based on these considerations, the dependent variable in this situation would be the distance the car has traveled (Option D). This is because the distance the car travels depends on the duration of the travel which makes it a dependent variable.
Answer: D. The distance the car has traveled