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: To control the expression of certain genes according to population density, bacteria use systems of: 
 Options:  <1> Strict response <2> Two components <3> Perception of the quorum. <4> Densitometric adaptation. <5> Negative activation
