Answer:
c) at the top of the balls trajectory
Step-by-step explanation:
If the ball is thrown at an upward angle, the ball will rise upwards to a certain highest point and then change direction and start to fall downwards. All this happens when the ball is also travelling horizontally, which causes the ball to travel in an arc.
If we consider the point where the ball reaches its highest point in its trajectory, we realize that at this point (where the ball actually switches directions from upward to downward), the ball actually momentarily pauses vertically (it still moves horizontally, but it is neither moving up or down)
At this point (i.e at the top of its trajectory), the ball has zero vertical velocity.