What about the structure of DNA allows it to copy itself? A. It is held together mostly by hydrogen bonds, which are easy to open for replication
B. It has enzymes built into the helix that make a copy when needed.
C. It is double stranded, so each side serves as a template for a new strand.
D. DNA is not copied, it is only passed down through each generation.

C. It is double stranded, so each side serves as a template for a new strand

Explanation:

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 -