(D) The ways that memory storage modifies the structure of the brain
(E) The kinds of training used to test memory enhancement in rats
20.The author refers to the results of the experiment using adrenergic antagonists as "negative findings" (line 13) most likely because the adrenergic antagonists
(A) failed to disrupt adrenaline’s effect on memory
(B) did not affect glucose’s ability to enhance memory.
(C) did not block adrenaline’s ability to increase blood glucose levels
(D) only partially affected adrenaline’s ability to enhance memory
(E) disrupted both adrenaline’s and glucose’s effect on memory