Glycolysis - Medical Science

Q1:

In glycolysis, ATP is formed by the transfer of a high-energy phosphate from 1,3-bisphosphoglycerate to ADR No such high-energy phosphate donor has ever been isolated in mitochondria because

A the techniques for isolating the phosphate donor are not refined enough

B no such phosphate donor exists

C the high-energy phosphate donor is very short-lived and difficult to isolate

D None of the above

ANS:B - no such phosphate donor exists

What's ADR? Please explain.