Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: What is the chemical basis for the reversible inhibition of acetylcholinesterase by the alkaloid physostigmine and related compounds ?: 
 Options:  <1> Allosteric inhibition of the enzyme. <2> Covalent binding to a cofactor essential for the reaction. <3> Coordination of an Mg2 + cation in the active center of the enzyme. <4> Analogy with the transition state of the reaction catalyzed by the enzyme. <5> Formation of a carbamate (carbamoylation) of the serine residue in the active center of the enzyme.
