The cognitive domain of learning encompasses intellectual skills and the acquisition of knowledge. It is concerned with a person's ability to process and comprehend information, which includes understanding concepts, remembering facts, applying knowledge, and solving problems. The example provided, understanding the growth rate of a wildland fire, is a classic cognitive task that requires knowledge, comprehension, and analysis. This domain focuses on what a person knows and understands, making it the correct answer.

A. Affective: This domain relates to feelings, emotions, attitudes, and values, not the intellectual process of understanding a concept like fire growth.

C. Psychomotor: This domain involves physical skills, coordination, and the manipulation of objects, such as operating a fire hose, not mental comprehension.

D. Didactic: This refers to a specific, instructor-centered method of teaching, not a domain of learning within the individual.

1. NFPA 1035, Standard for Fire and Life Safety Educator, Public Information Officer, Youth Firesetter Intervention Specialist, and Youth Firesetter Program Manager Professional Qualifications, 2015 Edition.

Section 3.3.3.2 Cognitive: "The cognitive domain relates to the recall or recognition of knowledge and the development of intellectual abilities and skills." This definition directly aligns with the question's focus on "what people understand."

2. SFPE Handbook of Fire Protection Engineering, 5th Edition, Springer.

Chapter 66, "Public Fire Safety Education," Section 66.4.1, "Educational Objectives," Page 2439: "Educational objectives are typically classified into three domains: cognitive (knowledge), affective (attitude), and psychomotor (skills). The cognitive domain deals with the recall or recognition of knowledge and the development of intellectual abilities and skills."

3. Armstrong, P., Bloom’s Taxonomy, Vanderbilt University Center for Teaching, 2010.

The guide describes the Cognitive Domain as including "knowledge and the development of intellectual skills. This includes the recall or recognition of specific facts, procedural patterns, and concepts that serve in the development of intellectual abilities and skills." This foundational academic source confirms that understanding concepts falls squarely within the cognitive domain. (Available at: https://cft.vanderbilt.edu/guides-sub-pages/blooms-taxonomy/)