Im pretty sure that this is the nerves which is called the nerves system I think
A n environmental stressor could be;
the weather, too hot, say a heatwave, which can cause heat stroke, dehydration etc, or too cold, where vulnerable people may freeze to death, or develop frost bite etc.
So, some characteristic part of where we live which may, under certain conditions cause difficulty for us or some other living being.
The joining of an egg and a sperm
The answer should be flexibility workout.
