Radiation is known to kill cells by damaging dna; how can radiation be controlled and safely used in medicine?

There are different types of radiation. Some harm us, some aid us, and some don't do anything to us at all. What radiation actually does in mutate the DNA. If you are the one applying the radiation you can control the mutation to be things that help the body.

b. the carbon cycle ensures living things have a source of hydrogen

straight or amphibians are homeothermic to thermal