When analyzing a source, historian has to remain unbiased and free from personal feelings and opinions. They know that there are different source of an event and they may reveal different facts which could cross-check his argument. The objective historiography is possible only when the historian is unbiased and when different sources like archaeological, literary and other sources are cross-checked and interpreted independently.
Because they belived the Manchos Dynasty had lost the Mandate of Heaven
That's A, President Franklin D. Roosevelt. The topic you're asking about is extremely important. I would delve into a bit more research. I can't remember why FDR but I did the test a while back and got an A.