When a Newspaper Editor Talks About "The Wall" with Respect

When a newspaper editor talks about "The Wall" with respect to in-house operations, he or she is referring to:

A) the difference between veteran and cub reporters.
B) the formal separation of the newspaper's editorial staff and sales force.
C) how difficult it is to access certain information from internal sources.
D) the separation of classified advertising from other types of advertising.
E) the lowest ad-placement rate accepted in the newspaper.