Answer: A. when energy is released!
Explanation: When a phosphate group is removed from an ATP, the ATP is converted to adenosine diphosphate (ADP). It also, to apply to your question, releases energy to form adenosine monophosphate (AMP).
Hope this helps, if not, comment below please!!!
(PS, I'm pretty new to this, so if I happen to be wrong, please tell me.)
:L
