A microscope that is calibrated this way will maintain the specimen in focus when the objective lens is rotated. ● Pointer
● C-mount
●fine focus
●Parfocal

The correct option is;

Parfocal

Explanation:

A perfocal lens is one that when in use, the object remains in focus when the  objective lens is rotated to change the magnification power of the microscope. That is the when the magnification is adjusted, the objectives remains in focus. The use of the parfocal lens however results in a small but insignificant amount of error in the focus.

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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what statement best describes the difference between the sympathetic and parasympathetic nervous systems?

the sympathetic nervous system prepares the body for intense physical activity and is often referred to as the fight-or-flight response. the parasympathetic nervous system has almost the exact opposite effect and relaxes the body and inhibits or slows many high energy functions.