Explanation :
The interaction between two objects is termed as the collision. The collision can be of two types i.e. elastic collision and inelastic collision.
In this case, two identical carts travel at the same speed toward each other, and then a collision occurs. In an inelastic collision, the momentum before and after the collision remains the same but its kinetic energy gets lost.
After the collision, both the object sticks over each other and moves with one velocity.
Out of the given graph, the graph that shows a perfectly inelastic collision is attached. It shows that after the collision both the carts move with the same velocity.