Detailed Instructions: 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'.
Problem:Question: How many macromolecular complexes form the electronic transport chain ?: 
 Options:  <1> 6 macromolecular complexes. <2> 5 macromolecular complexes. <3> 4 macromolecular complexes. <4> 3 macromolecular complexes. <5> 2 macromolecular complexes.
Solution:
3