What Is the Difference Between a Primary and a Secondary

What is the difference between a primary and a secondary academic reference?

A) Primary academic references include basic and applied research articles, whereas secondary academic references include review articles and academic book or textbook chapters.
B) Primary academic references are always longer than secondary academic references.
C) Primary academic references are peer-reviewed, while secondary academic references are not.
D) Primary academic references always contain facts, but secondary academic references do not.