Final answer:
The statement is true; hyphens are used in musical keys followed by the words flat, sharp, or natural but not with the words major or minor.
Step-by-step explanation:
The statement that you should "Use a hyphen when letters are used for musical keys that are followed by the words flat, natural, or sharp. If only the word major or minor is used, do not hyphen." is true. For instance, you would write A-flat, C-sharp, or G-natural, but you would write A major or C minor without a hyphen. This guidance is consistent with the rules for using hyphens in English to clarify the relationship between words in a compound modifier. When the terms flat, sharp, or natural follow a musical note, they function together as a single descriptive unit, modifying a noun that follows them. Therefore, a hyphen is used to join them. However, major and minor are not part of a compound modifier and stand alone without a hyphen when they are used with musical keys.