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'.
Input: Question: In suppression ion chromatography:
Options: <1> A single column is used and the conductivity of the mobile phase is kept very low. <2> The eluent must be able to be removed selectively after separation and prior to the conductometric measurement. <3> The eluent incorporates a regenerating solution of strong acid flowing in the same direction as the mobile phase. <4> Weak exchangers are used from polystyrene polymers. <5> A mobile phase with ionic conductivity gradient is used.
Output:
2