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: Which of the following chemical equilibria is heterogeneous? 
 Options:  <1> Acid-base balance. <2> Balance of complex formation. <3> Precipitation balance <4> Oxidation-reduction balance. <5> All those balances that take place in a single phase, usually liquid.
