Answer:
D. Freedom is so important that sometimes we must fight for it
Step-by-step explanation:
The Gettysburg Address was the speech delivered by Abraham Lincoln at the dedication ceremony for the national cemetery at Gettysburg. In his speech he recognized and honored the effort of the fallen soldiers in the American Civil War ongoing and gave encouraging words to continue the war because his aim was to convince Americans that the war was worth continuing, so the central idea can be summed up with the sentence: Freedom is so important that sometimes we must fight for it.
The following parts of the speech support that central idea: "It is for us the living, rather, to be dedicated here to the unfinished work which they who fought here have thus far so nobly advanced." and "(...) that we here highly resolve that these dead shall not have died in vain—that this nation, under God, shall have a new birth of freedom, and that government of the people, by the people, for the people, shall not perish from the earth."