Final answer:
In APA formatting, "A. Major causes" would be formatted as "I. Major Causes" with subtopics listed underneath with uppercase letters and a hierarchical indentation. The outline would utilize a combination of Roman numerals, uppercase letters, Arabic numerals, and lowercase letters to organize the content.
Step-by-step explanation:
When using APA formatting for an outline based on a previous outline developed with Roman numerals, the topic "A. Major causes" would be formatted according to APA guidelines for outlines. In APA, the main points of an outline use capitalized Roman numerals. Following the main point, supporting points and details use uppercase letters, Arabic numerals, and lowercase letters respectively.
To align with APA formatting conventions, after writing the Roman numeral for the main point, for the topic "Major causes", you would use an uppercase letter. For example, if "Major causes" is the first main point in your outline, it would be "I. Major Causes". Subtopics under this would then be listed as "A. Cause 1", "B. Cause 2", and so on, using a hierarchical structure of indentation to organize levels of detail beneath each main point.