English article styles are various.
To know those distinct styles is never an easy work.
However, I, eventually, almost figure them out after integrating them from several books about reading and writing.
The following information I gathered and integrated for a long time may be is helpful to those who are also confused by this section.
A. The Author’s Purpose and Modes of Discourse
1. Illustration (expository)
6. Problem-solving (Question and Answer)
14. Mixed Modes of Discourse
B. Methods of Paragraph Development
1. Cause and Effect
2. Comparison and Contrast
3. Definition and Example
4. Examples and Illustration
5. Classification (Classification and Analysis)
6. Fact and Opinion
7. Facts and Statistics
8. Process Analysis
C. Patterns of Organization Defined
2. Chronological / Spatial / Deductive / Inductive order
3. Order of Importance / Time / Space / Location
Part B and Part C maybe can be seen as the same meaning. i, however, saw the content of one book about reading takes them apart just like I wrote above. Hence, I believe those two parts remain have different nuances.