Which of the following is included in the types of parties that may be served?

The correct response highlights the diversity of entities that can be served legal documents, specifically focusing on natural persons and sole proprietorships. Natural persons refer to individual human beings, who can be served with legal papers as they have full legal capacity to enter into contracts and can be held liable in civil proceedings. Sole proprietorships, while often considered a business entity, are still closely tied to the individual owner; thus, any legal action directed at a sole proprietorship also effectively involves the owner personally.

Understanding this context is crucial in civil process because legal actions frequently initiate against individuals in their personal capacity or against their businesses, which are directly linked to them. This option encompasses the most fundamental categories of parties in civil process, ensuring that legal documents reach those who are accountable for the actions being litigated.

Other options, while they represent entities that can be served, do not encapsulate the breadth of parties that may be involved in legal proceedings, particularly the direct involvement of individual persons and sole proprietorships in the legal system.