In the Presence of Pentazocine , a Higher Concentration of Morphine

In the presence of pentazocine , a higher concentration of morphine is required to elicit pain relief . Pentazocine by it self has a smaller analgesic effect than does morphine , even at the highest dose , Which of the following is correct regarding these medications ?

A) Pentazocine is a competitive antagonist .
B) Morphine is a full agonist , and pentazocine is a partial agonist .
C) Morphine is less efficacious than is pentazocine .
D) Morphine is less potent than is pentazocine .
E) Pentazocine is a noncompetitive antagonist .