which ozone in the upper atmosphere is beneficial to humans ,ozone at ground level is dangerous because

Stratospheric ozone is good because it protects living things from ultraviolet radiation from the sun. Ground-level ozone, is bad because it can trigger a variety of health problems, particularly for children, the elderly, and people of all ages who have lung diseases such as asthma.

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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that is wrong, its not thymus.