This question tests knowledge of terms related to publications. The correct answer is 'A. readership,' which refers to the group of people who read a particular publication. Option B, 'incorporate,' means to include or contain within something else, which is unrelated to the number of readers. Option C, 'separate,' means to divide or keep apart, which is not related to readership. Option D, 'primacy,' means the state of being first or most important, which does not relate to the number of readers.