Answer:
The correct answer is civilians.
Explanation:
War bonds are debt instruments issued by a government during times of war, in order to raise money to finance military operations. These bonds are bought by civilians - by purchasing them, they lend money to the government, who will repay them at a later date plus interests. In the last two world wars, the governments of the Western allies issued war bonds, and encouraged the general public through propaganda such as posters and comic books to join the war effort by buying them.
Civilians. It wouldn't apply to American Soldiers since they are the ones being paid for. It wouldn't apply to the Germans either, since they aren't paying for the enemy to fight them.
too biased for historical evidence
too focused for historical evidence
unreliable narrative source
useful primary source document
The answer is: effective secondary source document"
Within 20 years, historians would have enough time to gather all facts and data from all sides that involved in historical event. All of these facts and data is useful for them to decipher how the historical events were unfolded.
This make the chart an effective source to find for information regarding the event. But, since it does not made by people who actually involved in the events, it could only be considered as a secondary source.