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

[Q]: Radioisotopes may vary greatly in their rate of decay, decaying faster if their nuclei are more what?
[A]: unstable

[Q]: What do we call the diffusion of water across a membrane because of a difference in concentration?
[A]: osmosis

[Q]: What is the term for a resource that is used in a way that meets the needs of the present without keeping future generations from meeting their needs?
[A]:
sustainable