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.

Question: Ultraviolet radiation changes the structure of DNA by: 
 Options:  <0> Rupture of phosphodiester bonds. <1> Deamination of nitrogenous bases. <2> Depurinization <3> Formation of cyclobutyl rings of pyrimidines. <4> Hydroxylation of nitrogenous bases.
chemistry