Answer:
Instead of oxygen a creature would also need nutrients. Simple everyday things like water and food.
Explanation:
Although it is kind of impossible to live without oxygen. There are organisms on the earth who do not need it and can survive. They metabolize hydrogen or methane or a number of other compounds.
I think personal it is 6 but maybe other people have a better answer <span />
Answer:
The body has two lines of natural defense to protect against infection. The first are physical barriers, such as the skin, body secretions and mucous membranes. The second line of defense is the immune system. Specialized immune cells coordinate and execute attacks to kill germs that make it past the body's physical barriers.
