Weathering physically breaks rock down into smaller pieces called

Mechanical or physical weathering breaks down the rocks into smaller pieces, called sediment.

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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i might be wrong but i think its a. let me know if i’m right and have a good rest of your day!