The purpose of etymology is to explain how a word has changed or evolved over time. By studying the origins and historical development of words, etymology provides insights into the meaning and usage of words. To find the correct answer, we can eliminate options that are not directly related to the historical aspect of words. Option 1, "to explain the meaning of a word," does not specifically mention the historical element. Option 2, "to learn how to spell a word correctly," is focused on spelling, which is not the primary concern of etymology. Option 3, "to understand how sounds are produced in a language," is more related to phonetics and linguistics, rather than the historical aspect of words. Finally, option 4, "to tell how a word has changed or evolved," directly addresses the historical aspect of words and aligns with the purpose of etymology. Therefore, the correct answer is option 4.
