Final answer:
The cart is moving at a constant speed.
Step-by-step explanation:
The statement that best describes the cart is b) The cart is moving at a constant speed.
If the position of the cart during the 7-second time interval is graphed, and the graph shows a horizontal line, then the cart is not changing its position, meaning it is not stationary (a). If the graph shows a straight line with a constant slope, then the cart is moving at a constant speed (b). Acceleration would be represented by a curved line on the graph, indicating that the speed is changing over time (c). An irregular motion would be represented by a graph that does not follow any pattern or consistent trend (d).