Most popular historical films are not documentaries; they are dramatic presentations of historical events.
Conclusion (consequently)
Uninformed viewers of dramatic historical films should not regard them as accurate portrayals of historical events.
Evidence
Most popular historical films are dramatic presentations of historical events, not documentaries. Such presentations cannot present the evidence for the accuracy of what they portray.
Evaluate
The conclusion cares about whether or not we "should regard X as an accurate portrayal". The reason the author doesn't think we should consider historical films accurate portrayals is that they are not documentaries, they are dramatic presentations, and they cannot present the evidence for the accuracy of what they portray.
Goal
The correct answer can potentially use any of the things we know about historical films and then help us link that to "should not regard as accurate".
- If it's not a documentary, should not regard as accurate portrayal - If it's a dramatic presentation of historical events, should not regard as accurate portrayal - If the evidence for accuracy can't be presented, should not regard as accurate portrayal