Lead.
"Due to insufficient water treatment, lead leached from water pipes into the drinking water, exposing over 100,000 residents to elevated lead levels."
Natural selection allows nature to chose which species survives. Only the fittest get to pass on their genes. And by fittest i mean the ones that are better adapted to the environment.<span />
Water, air, food. and heat.
Well, the snails probably can't live in water, so what they needed was oxygen.
well it's not A, not C and not D.
The answer is most likely B
