Mrs Jennings Takes a New Medication, in Addition to Several

Mrs. Jennings takes a new medication, in addition to several she has used for years. The new agent is fairly effective, but it seems to interfere with the action of an older drug that normally has greater efficacy. Mrs. Jennings' new drug is apparently acting as a:

A) partial antagonist.
B) competitive antagonist.
C) noncompetitive antagonist.
D) partial agonist.
E) none of the above.