Structure-activity studies of cholinergic drugs indicate that:

Structure-activity studies of cholinergic drugs indicate that:

I. maximum activity is achieved when the quaternary nitrogen is three carbons removed from the ester oxo group.

II. structures which display a quasi-ring conformation exhibit muscarinic activity.

III. one methyl group of the trimethylammonium group can be replaced by an ethyl group with only slight loss of activity.
A . I only
B . III only
C . I and II only
D . II and III only
E . I, II and III

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Answer: D