Final answer:
President Obama's central message revolved around active citizenship and the individual's role in preserving democracy, aligning with option A.
Step-by-step explanation:
The central idea of President Obama's address can be understood through the lens of the expectations set by his campaign and the civic responsibilities he encouraged. One of the main themes seen throughout his presidency and addresses was the importance of active citizenship in preserving democracy and the necessity for each generation to take up the torch of societal progress. Considering his emphasis on a collective moral responsibility and the civic engagement to uphold and advance societal values, the statement that best describes the central idea of President Obama's address is likely A. American citizens are individually responsible for preserving democracy.