There are three velocity-time graphs. You must choose which is /are representative of an object that is changing directions. The way to think about these graphs is described below.
Velocity-Time Graphs: And a sloped line (whether straight or curved) is an indication of a changing velocity motion. A line in the + region of the v-t graph is an indication that the object is moving in the positive (rightward) direction. And a line in the - region of the v-t graph is an indication that the object is moving in the negative (leftward) direction. If an object is changing direction, then the line must pass across the time axis (i.e., the v=0 m/s mark). This means that changing directions corresponds to a line that is in the + region at one point in time and in the - region of the graph at another point in time.
Don't Be Confused: Students can definitely get confused by this question. They hear the term "chaning directions" and begin hunting for a line that changes direction. That is, they look for a line that bends, thinking that is all that matters. But don't be confused. If a line slopes down and later slopes up, then the line has changed directions. But this doesn't mean the object has changed directions! For a moving object to change directions, it must be moving in one direction at one moment and in a different direction at another moment. Right? Right! So one a velocity-time graph, the direction that an object is moving at a given moment is represented by where the line is located at that moment. That is, if the line is above the time axis, the object is moving in the + direction; and if the line is below the time axis, then the object is moving in the - direction. So changing directions means that the line on the velocity-time graph must cross over the time axis from the + region to the - region or vice versa.