Consider these four line graphs representing speed in meters/second, where each X-axis is labeled in seconds and each Y-axis is labelled in meters.
Which graph represents an average speed of 1.57 m/s?
A)
X
B)
C)
D

Answer : (A) They all indicate a constant speed.  

Explanation :

In this case, four line graphs represent speed in m/s. The x-axis is labeled in seconds (time) and the y-axis is labeled in meters (distance).

The slope of the distance-time graph gives the slope. It can be seen from the attached figure that, in each case, the speed is constant everywhere.  

Hence, the correct option is (A) " They all indicate a constant speed ".