Which of the Following Explains Why Media Planners Have Difficulty

Which of the following explains why media planners have difficulty measuring the effectiveness of advertising and promotions?

A) The media planner must usually balance quantitative data with subjective judgements based on experience.
B) An opportunity to advertise within a new media vehicle might arise, requiring movement of advertising dollars from one vehicle to another.
C) Procurement specialists often put pressure on the media decisions in an effort to save money.
D) There is a debate as to whether media planning buying should be part of an advertising agency or an independent agency.