The answer is A: to inform.
Explanation for each option:
A. To inform: This is often the primary purpose of writing about a concept. When the goal is to inform, the writer aims to provide the reader with factual information and a clear understanding of the concept. This involves presenting data, evidence, and explanations to enhance the reader's knowledge.
B. To explore: While exploring a concept can be a purpose of writing, it is more about examining different aspects or perspectives of a concept rather than providing straightforward information. Exploration might involve questioning and investigating rather than simply informing.
C. To argue: Writing to argue involves taking a stance on a particular issue or concept and persuading the reader to accept a particular viewpoint. This is different from merely informing, as it involves presenting arguments and counterarguments.
D. To explain: Explaining is closely related to informing, but it often involves breaking down complex ideas into simpler terms. While explaining can be a part of informing, the primary purpose of writing about a concept is generally to provide information, which may include explanations as a component.