Read the following passages. each source is related to the 1858 debates between stephen a. douglas and abraham lincoln for a seat in the united states senate. which of the following describes a common feature of each of these sources?

source 1
over 150 years ago, abraham lincoln and stephan a. douglas held seven debates as they campaigned for a senate seat in illinois. the debates focused on the issue of slavery and its expansion into the territories. douglas overturn the prohibition on slavery in the territories of kansas and nebraska with the kansas-nebraska act. referred to as popular sovereignty, citizens in kansas and nebraska, not the federal government, could determine whether slavery should be allowed to exist in these territories.

source 2
"that is the real issue [with the question of slavery]…it is the eternal struggle between these two principles-right and wrong-throughout the world. they are the two principles that have stood face to face from the beginning of time; and will ever continue to struggle. the one is the common right of humanity and the other the divine right of kings. it is the same principle in whatever shape it develops itself. it is the same spirit that says, ‘you work and toil and earn bread, and i'll eat it.’ no matter in what shape it comes, whether from the mouth of a king who seeks to bestride the people of his own nation and live by the fruit of their labor, or from one race of men as an apology for enslaving another race, it is the same tyrannical principle.”

—abraham lincoln, during the seventh debate with stephen a. douglas
a. both are secondary sources that summarize lincoln and douglas's important opinions.
b. both are valuable to a historian as well-written primary source documents.
c. both could be used to support a historical argument about the lincoln-douglas debates.
d. both indicate that douglas's opinions on race were the opposite of lincoln's.