Answer:
water vapor, carbon dioxide, and sulfur gases (and ash, during an eruption and depending on the volcano).
A stem cell is a cell that has layers of bacteria that helps protect the water that follows through it.
Darwin's theory of evolution by natural selection can explain how antibiotics are becoming defective because the bacteria that is trying to be fought off might have had a mutation making it more likely to survive. Once that surviving bacteria makes offspring most of the first generation will die from the antibiotic but soon all of their offspring will produce a resistance to that antibiotic.
