The two sounds heard through the stethoscope during a heartbeat are known as lub and dub. If the doctor detects an unusual lub sound, evaluate which description could explain the atypical sound.
A)
The aorta extends during the systolic phase.
B)
The mitral valve does not close after the systolic phase.
The aortic valve does not close during the diastolic phase.
D
The pulmonic valve does not close during the diastolic phase.

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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just finished the test, the answer is d, greg is the least cost-effective because he charges the most for the project

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.