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: Consider Input: Question: Reactivity is considered a source of error when using Observation as a method of obtaining information. Where does it come from?
Options: <1> From the context in which the Observation is generated. <2> Of the observed subject. <3> Of the chosen procedure. <4> From the observer. <5> Of the type of instrument chosen.

Output: 2

Input: Consider Input: Question: If you want to estimate the effects of an intervention, you will use:
Options: <1> A transversal design. <2> A retrospective design <3> An ecological study. <4> A randomized clinical trial. <5> An observational design with random selection of the participants.

Output: 4

Input: Consider Input: Question: On the link between the nitrogenous base and the ribose of the nucleotides:
Options: <1> The anomeric carbon of ribose is in alpha configuration. <2> It is an N-glycosidic bond. <3> It involves the C5' of the ribose. <4> It involves phosphate groups. <5> It is of a different nature for each nitrogenous base.
Output: 2