5) from an environmental perspective, it is important to ensure that radioactive materials are stored properly, because radioactive samples:
a) can be in liquid, solid or gas forms
b) once they are leaked into the environment, could cause serious health hazards to all living organisms
c) can remain radioactive for long periods of time
d) can do all of these

can do all of these

Explanation:

A radioactive material may exist in any given state of matter; solid, liquid or gas. Some radioactive materials have very long half lives. Half life refers to the period of time it takes for the amount of radioactive material in a sample to decrease by half of its original content of radioactive material.

Most radioactive materials produce ionizing radiation which causes ill effects on human and animal cells.