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'.

[EX Q]: Question: The determination of cyanide by the Liebig method is based on the addition of a silver nitrate standard solution: 
 Options:  <1> Until complete precipitation of silver cyanide. <2> Until the precipitation of silver cyanide begins. <3> Until the appearance of a red precipitate of silver chromate. <4> Until the AgCN complex is quantitatively formed. <5> Until the precipitation of silver iodide, yellow.
[EX A]: 2

[EX Q]: Question: The placenta is a derivative of: 
 Options:  <1> The zona pellucida. <2> The trophoblast. <3> The ectoderm <4> The mesoderm <5> The primitive line.
[EX A]: 2

[EX Q]: Question: Crohn's disease: 
 Options:  <1> It only affects the colon. <2> It presents as perianal disease, with development of fistulas or abscesses. <3> It is characterized by continuous involvement of the mucosa. <4> It is associated with alcohol consumption. <5> It starts in the infant stage of the individual.
[EX A]:
2