You are given a paragraph, with numbered sentences, and a question. Write the numbers of the sentences needed to answer the given question. Separate multiple sentence numbers with a comma (", "). E.g. "1, 2" would be the correct response if Sent 1 and Sent 2 are needed to answer the given question (do not include sentences that contain no information that is necessary to answer the question). Sort the sentence numbers in an increasing order (i.e., '1, 2', instead of '2, 1'). Your answer should not contain anything than the sentence numbers separated by a comma (e.g. '1, 2, 3, 4'). The given question requires more than one sentence to answer. So, your answer must contain at least one comma (", ").

Paragraph- Sent 1: What happens when a diver jumps off the diving board?
Sent 2: His gravitational potential energy changes to kinetic energy as he falls.
Sent 3: In other words, he falls faster and faster until reaching the water.
Sent 4: However, he can always regain his potential energy.
Sent 5: All he must do is get out of the water and climb back up.
Sent 6: This requires an input of kinetic energy.
Sent 7: These changes in energy are examples of energy conversion.
Sent 8: Energy can be converted from one form to another.
Sent 9: It can also be transferred from one object to another.
Sent 10: Think back to the leaf example.
Sent 11: The leaf was hanging from a branch.
Sent 12: At this time, it had gravitational potential energy.
Sent 13: As it came loose from the branch, gravity pulled it toward the ground.
Sent 14: The leaf started to fall, or move, toward the ground.
Sent 15: Its potential energy was changed into motion.
Sent 16: As it landed on the ground, it stopped moving.
Sent 17: As it lays on the ground, it has no potential to move.
Sent 18: If it does move it is because something else transferred energy to it. 
Question: Before a diver dives after a diver board or before a leaf falls from a branch and remains hanging, there is what type of energy?.

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
1, 2, 11, 12.