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'.

Example Input: Question: We want to study if Vitamin D can increase the incidence of breast cancer. In our area we have a population registry of cancer. To achieve our goal, all women diagnosed with breast cancer are selected from the register we have and each case pairs with two controls. What study design has been chosen? 
 Options:  <1> Prospective cohort study. <2> Cases and controls study. <3> Case-control study nested. <4> Retrospective cohort study. <5> Ecological study
Example Output: 3

Example Input: Question: If, by adding a drop of H2O2 to a bacterial suspension, bubbles (O2) are generated, the bacteria produce: 
 Options:  <1> Cytochrome C oxidase. <2> Oxygenase <3> Superoxide dismutase. <4> Catalase <5> Anhydrase
Example Output: 4

Example Input: Question: The ionization source known as Inductive Coupling Plasma used in Elemental Mass Spectrometry, is characterized by: 
 Options:  <1> Generate mostly monatomic ions. <2> Fragment the organic molecules in molecular ions that allow their identification. <3> Be a low energy source. <4> Run at high vacuum. <5> Reach detection limits of the order of mg L-1 for most elements.
Example Output:
1