Final answer:
George Washington was the first president of the United States. Lincoln's main concern in his first Inaugural Address was the possible onset of a civil war, focusing on union continuity and opposing secession. The correct answer is A. a possible civil war.
Step-by-step explanation:
The first president of the United States was George Washington. However, the question also asks about Abraham Lincoln's concerns at the time of his first Inaugural Address. According to Lincoln’s “Second Inaugural Address”, the issue that predominantly occupied people's thoughts and attention at the time of his first Inaugural Address was a possible civil war. This is inferred from Lincoln's focus on the continuity of the Union, the legality of secession, and his position on slavery during his first Inaugural Address.
He expressed that he would not interfere with the institution of slavery in the states where it existed but was firmly against the expansion of slavery into new territories and opposed secession, underlining the permanent nature of the Union.