**Explanation:**

A distance-time graph represents the relationship between the distance traveled by an object and the time taken to travel that distance. The slope of a distance-time graph represents the speed of the object.

**Understanding Slope:**
The slope of a line on a graph represents the rate of change between two variables. In the case of a distance-time graph, the slope represents the rate at which the distance traveled changes over time.

**Interpreting the Slope:**
The slope of a distance-time graph can be calculated by dividing the change in distance by the change in time. This gives us the speed of the object.

For example, if the distance traveled increases by 10 meters in 2 seconds, the slope would be 10/2 = 5 meters per second. This tells us that the object is traveling at a speed of 5 meters per second.

**Relationship to Speed:**
Speed is defined as the distance traveled per unit of time. Therefore, the slope of a distance-time graph represents the speed of the object. A steeper slope indicates a higher speed, while a shallower slope indicates a lower speed.

**Relationship to Other Quantities:**
While the slope of a distance-time graph represents speed, it does not directly represent other quantities such as distance, momentum, or velocity. These quantities may be related to the speed, but they are not directly represented by the slope of the graph.

- Distance: The distance traveled can be determined by looking at the y-intercept of the distance-time graph, not the slope.
- Momentum: Momentum is defined as the product of an object's mass and velocity. It is not directly related to the slope of a distance-time graph.
- Velocity: Velocity is a vector quantity that includes both speed and direction. The slope of a distance-time graph represents speed, but not the direction of motion.

Therefore, the correct answer is option 'B' - the slope of a distance-time graph represents the speed of the object.