Drug S is most like
The effects of Drug S are changed by treatment with the beta blocker, but not by the alpha blocker (choices A, C, and D are ruled out). Terbutaline is beta2 selective and would not increase heart rate directly. Drug S is isoproterenol.
Epinephrine
Isoproterenol
Norepinephrine
Phenylephrine
A.N.S.