One of the History Teachers Below Is Violating a Principle

One of the history teachers below is violating a principle recommended for classroom lectures.Which one?

A) Mr.White explains to his students how wars between countries are in some ways similar to the fights children have with one another.
B) Ms.Bartlett begins her discussion of the American Civil War by drawing some parallels between it and something the class has already studied-the American Revolution.
C) During a unit on World War I, Mr.LeMessurier often uses maps to show how certain battles were fought at especially strategic locations.
D) Ms.Volchoff talks in a relaxed conversational style, describing different battles of World War II as they come to mind.