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

[EX Q]: What is the basic structure that holds plants upright, allowing plants to get the sunlight and air they need?
[EX A]: stem

[EX Q]: What is the evolutionary history of group of related organisms
[EX A]: phylogeny

[EX Q]: What is the low level of radiation that occurs naturally in the environment called?
[EX A]:
background radiation