In this task, you are given a question and answer options for that question. Using this information, you have to classify each text into different topics: medicine, nursery, psychology, chemistry, pharmacology, biology.

[EX Q]: Question: Esters can be obtained from carboxylic acids and alcohols, by applying the Fischer esterification reaction in which: 
 Options:  <0> A base is used as a catalyst. <1> A ketone is used as the solvent. <2> A reducing reagent is used. <3> An oxidizing agent is used. <4> Acid catalysis is used.
[EX A]: pharmacology

[EX Q]: Question: A rat pathogen that has fleas as vectors of transmission to humans is: 
 Options:  <0> Rickettsia rickettsii. <1> Yersinia pestis <2> Borrelia burgdorferi. <3> Ehrlichia ewingii. <4> Brucella abortus.
[EX A]: biology

[EX Q]: Question: The tungsten is a very important element from the technological point of view, which is used, among other things, in the steel industry. But his interest extends to other scientific fields, due to: 
 Options:  <0> Which is one of the essential elements for life are human beings and animals. <1> Which is liquid in the range 27ºC-2500ºC, which explains its use in high temperature thermometers. <2> Its inability to react with oxygen even at such high temperatures as heating to red. <3> Its total resistance to fluoride even at temperatures as high as heating to red. <4> Its great mechanical resistance.
[EX A]:
chemistry