the answer is b...........................................................
I got the same answer as you so try picking the answer that is closest to the answer you got sorry i couldn't help much
Oxygen and glucose at top
carbon dioxide and water at bottom
The variable is the group that was given caffine, because thats what the doctors manipulated. They possibly altered the natural memory of the participants by giving them caffine. A more specific variable could be how much caffine each participant is given and what time are they given it.
