Final answer:
Each subdivision of an outline should have at least two parts in order to provide clarity, support, and depth to the main points being presented.
Step-by-step explanation:
In an outline, each subdivision should have at least two parts for several reasons. Firstly, it helps to provide clarity and structure to the overall organization of the outline. Secondly, it ensures that there is enough information and support for each main point or idea being presented. For example, if there is only one part in a subdivision, it may not provide enough depth or evidence to fully explain the main point.