You are developing an application that will allow users to read and post comments on news articles. You want to configure your application to store and display user-submitted comments using Firestore. How should you design the schema to support an unknown number of comments and articles?

A. Store each comment in a subcollection of the article. B. Add each comment to an array property on the article. C. Store each comment in a document, and add the comment's key to an array property on the article. D. Store each comment in a document, and add the comment's key to an array property on the user profile.