At which phase can we see none of the lighted half of the moon?

New Moon

Explanation: So you are not confusing this with 'full moon'. Think of the new moon as what it says, a new moon. By the phases, the new moon gains light, until it reaches 'full moon', where the moon is FULL of light.

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.  

read more on -

b - the respond is innate and varies over time.

good luck!