It seems to me that the answer here moves you into a bit into postmodern territory. My guess is that your module has probably examined how one particular historical event can be seen in different lights. History is not a single story because there are multiple experiences and multiple narratives that emerge from one specific historical event. For example, if one takes any historical event, there are different perspectives from which that event can be told. Some might be from the point of view of the perpetrator, while others might be from the point of view of the victims, and others might be from the bystander, or even people who are removed from it with the passage of time, but have something to say about it. With this, history is not a single story, but rather multiple narratives woven together in a single event. The memory that one has of history is determined by many elements. One of which is who possesses the power to tell history. For example, there are those who might benefit if a particular narrative or story from history is erased or not told. Think of the current situation in Syria. It benefits President Assad if his state controlled media silences the voices of the opposition and prevents its story from emerging. The memory element of history is how many of the stories from events and occurrences are able to survive and be heard. It is here where I think that it becomes clear that history is not and, frankly, should not be a single story. It is more of a tapestry of different stories woven together to better understand both memory and human consciousness.