How does oxygen move from the respiratory system to the circulatory system?
O A. By moving across a synapse
O B. By pumping through the heart
O C. By circulating in an artery
D. By diffusion across a capillary wall

D. By diffusion across a capillary wall

Explanation:

D is the best answer because gas exchange takes place in our lungs. Our lungs have alveoli which have a network of tiny blood vessels called capillaries, here the O2 diffuses the capillary wall to enter the bloodstream, and similarly CO2 diffuses out and we exhale it our from our lungs.

well we can't tell you because we cant see the time give a screen shot or something.

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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