Without the specific context or content of the article, it’s challenging to definitively determine the author’s purpose. However, based on the options provided, the most likely purpose could be inferred by considering the focus of the article.
If the article discusses classification, then "to explain how to classify living things" could be the purpose. If it involves food production and energy, then "to explain the production of food and how life uses energy" might be more appropriate. If the focus is on the roles of flies and maggots in an ecosystem or process, then "to explain the importance of flies and maggots" would fit. Lastly, if the content relates to disproving spontaneous generation, then the last option would apply.
In many scientific articles discussing biology, a popular focus may be on dispelling older theories or emphasizing the role of certain organisms. If the article discusses historical experiments, then "to explain past experiments that disproved spontaneous generation" could be the best choice.
To choose the most accurate purpose, consider the central theme of the article.