The answer in this question is an increase in the number of synapses. The changes that observe in the neural circuit when the gill-withdrawal reflex of the sea snail Aplysia has been successfully conditioned to a stimulus such as squirt of water from a Waterpik include an increase in the number of synapses.
I would say "difficulty to remove the atoms"
Hope this was helpful!! :)
Stomach,that pretty much all I know
Yes humans are part of the environment.
