Given a scientific question, generate a correct answer to it.

[EX Q]: Lampreys use their sucker to feed on what part of other fish species?
[EX A]: blood

[EX Q]: What are required when the damage from trauma or infection cannot be closed with sutures or staples?
[EX A]: skin grafts

[EX Q]: What force increases a slide downhill and decreases a slide uphill?
[EX A]:
gravity