What is the typical joint involvement with rheumatoid arthritis?
a) random single joints, progressing to involve other joints
b) bilateral small joints, symmetrical progression to other joints
c) abused or damaged joints first, then joints damaged by compensatory movement
d) progressive degeneration in selected joints

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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the answer is a) a shiprock was formed by igneous process