In the presence of naloxone, a higher concentration of morphine is required to elicit full pain relief. Naloxone by it self has no effect . Which of the following is correct regarding these medications?
(A) Naloxone is a competitive antagonist
(B) Morphine is a full agonist , and naloxone is a partial agonist
(C) Morphine is less efficacious than is naloxane
(D) Morphine is less potent than is naloxone
(E) Naloxone is a noncompetitive antagonist