Which of the following statements is true regarding the Advisory Opinions in relation to USPAP?

Advisory Opinions, as they relate to USPAP, serve as guidance but are not part of the mandatory standards themselves. They provide insights and interpretations to help appraisers understand and apply USPAP in various scenarios; however, they do not carry the weight of mandatory requirements. Therefore, the correct answer emphasizes their role as supplementary material rather than as foundational to USPAP, which is why they are not included in the USPAP publication.

While the other options mention aspects such as mandatory appraisal requirements or training purposes, these do not accurately represent the nature of Advisory Opinions. They are intended to offer advice rather than impose rules, making it crucial for appraisers to differentiate between what is mandatory and what is advisory.