An aurora is produced when there is a collision between and in earth's upper atmosphere.
a. atoms; molecules
b. light; atoms and molecules
c. neutrinos; atoms and molecules
d. the solar wind; atoms and molecules

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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b. lithosphere, asthenosphere, mesosphere   is the answer most likely