What Is the Focus of Advertising Agencies

What is the focus of advertising agencies?

A) They usually require advertisers to sign long-term contracts.
B) They prefer to work with local advertisers rather than national advertisers.
C) They compete against the national media for the business of big advertisers.
D) They do little more than sell media time or space to advertisers.
E) They are specialists in planning and handling mass-selling details.