Answer:
b. at the top
Step-by-step explanation:
At the top of the climb, the vertical velocity of Jeff's throw has a value of zero. 
Vertical velocity in this instance is acting against the acceleration due to gravity. 
- At the top of the thrown, the force of the throw becomes zero and the velocity also becomes zero. 
 - As the body finds it way downward, it begins to fall freely. 
 - The fall is due to the acceleration due to gravity which is experienced by every object on earth.