The question asks about interpreting a graph of speed (in miles per hour) as a function of time (in hours). Here's how to complete the dropdown choices:

• When the graph is increasing: The speed is increasing.
  This is because an increasing graph of speed over time indicates that the vehicle is accelerating or gaining speed.

• When the graph is decreasing: The speed is decreasing.
  This is because a decreasing graph of speed over time indicates that the vehicle is decelerating or losing speed.

This interpretation is based on the direct relationship between the slope of the graph and the change in speed over time.

Would you like a deeper explanation or examples? Here are some related questions for further exploration:

1. How can you determine acceleration from the slope of a speed vs. time graph?
2. What does a flat (constant) graph of speed vs. time indicate?
3. How is the area under a speed vs. time graph interpreted in physics?
4. What happens to the speed when the slope of the graph becomes negative?
5. How would you model speed changes using a mathematical function?

Tip: Always check the axes carefully on graphs to confirm what quantities are being plotted and in what units!