Which method would you use to find a single document in MongoDB?

The method used to find a single document in MongoDB is findOne(). This function is specifically designed for retrieving a single document from a collection that matches the specified query criteria. When you call findOne(), MongoDB searches the database and returns the first document it finds that meets the criteria provided. This is particularly useful when you need to ensure that only one document is returned, as it streamlines the retrieval process by preventing unnecessary loading of additional data.

In contrast, other options listed are not valid MongoDB methods. For example, getDocument(), selectSingle(), and retrieveDoc() do not exist in the MongoDB API, and thus cannot be used to interact with the database effectively. Understanding these foundational concepts is crucial as you work with MongoDB, allowing you to use the correct functions for data retrieval and manipulation.