Answer:
A / D
Explanation:
It can only provide energy for brief periods of time—eight to ten seconds. The system can be accessed a number of times, but will eventually exhaust the “built-in” supply of ATP - even with the help of the Creatine Phosphate molecule. And it's energy density is incredibly low. It is a big molecule with a molecular weight of 507. yet all the usable energy is in the two terminal phosphate groups.
