Final answer:
A new Word document defaults to the Office 2013 style set, which is the standard for new documents and a base for writing business documents.
Step-by-step explanation:
By default, a new Word document uses the style set Office 2013. This style set is applied to all new documents in Microsoft Word unless it is changed manually by the user. Learning how to write business documents, such as business letters, involves understanding the default formatting and style options available in Word, and the Office 2013 style set provides a standard starting point for document creation.