Answer:
A closed circuit doesn't allow the flow of electrons. an open circuit does. example: if you turn off a switch in your house. you 'broke the circuit it is closed.
<em>Homo sapien ((human))</em>
<em>Bat ((mammal))</em>
<em>aliigator ((reptilious))</em>
<em>Frog ((amphibious))</em>
<em />Fish
Two examples of radioisotopes that can be used are carbon-14 to determine the age of fossils. Second, we can use iodine-131 to treat thyroid disease.
