Given a scientific passage and an answer, generate a question for the given answer.

Ex Input:
Passage: Figure 2.43 Positions and velocities of a metal ball released from rest when air resistance is negligible. Velocity is seen to increase linearly with time while displacement increases with time squared. Acceleration is a constant and is equal to gravitational acceleration. Answer: acceleration

Ex Output:
If a ball is released from rest when air resistance is negligible, velocity is seen to increase linearly, while what related property is a constant?

Ex Input:
Passage: When two plates of continental crust collide, the material pushes upward. This forms a high mountain range. The remnants of subducted oceanic crust remain beneath the continental convergence zone. Answer: high mountain range

Ex Output:
When two plates of continental crust collide, the material pushes upward and forms what?

Ex Input:
Passage: Fractures are breaks in bone, usually caused by excessive stress on bone. Fractures heal when osteoblasts form new bone. The animation at this link shows how this happens: http://www. youtube. com/watch?v=qVougiCEgH8 . Soon after a fracture, the body begins to repair the break. The area becomes swollen and sore. Within a few days, bone cells travel to the break site and begin to rebuild the bone. It takes about two to three months before compact and spongy bone form at the break site. Sometimes the body needs extra help in repairing a broken bone. In such a case, a surgeon will piece a broken bone together with metal pins. Moving the broken pieces together will help keep the bone from moving and give the body a chance to repair the break. Answer: fractures

Ex Output:
What is it called when breaks in bone occur that is usually caused by excessive stress on the bone?