Answer:
The bias present in propaganda material.
Step-by-step explanation:
Advertising is a specific systematic way of persuading in order to influence ideological, political ends the emotions, attitudes, opinions or actions of the target audience. For this reason, if you include a collage of Cold War era propaganda, your research will not be unbiased, because the propaganda will have a bias towards one side of the war and will not bring an impartial and accurate message.