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.

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.

A: biology
****
Q: Question: The ketone bodies: 
 Options:  <0> They are used by the liver to synthesize fatty acids. <1> They only form in conditions of good nutrition. <2> Its formation is especially active in skeletal muscle. <3> It is formed from acetyl-CoA. <4> They never give acetone.

A: biology
****
Q: Question: What is the most common malignant tumor of the thyroid? 
 Options:  <0> Oxyphilic carcinoma <1> Papillary carcinoma <2> Follicular carcinoma. <3> Anaplastic carcinoma <4> Spinal carcinoma

A:
medicine
****