Based on the platforms outlined in sources 1 and 2, the correct answer would be:
B. Citizens' rights should be protected.
Both parties emphasize the protection of citizens' rights, with the Republican platform supporting citizenship protections for all citizens (native or naturalized) and the Democratic platform stating it is the duty of the U.S. to protect all its citizens, whether at home or abroad.
Options A and C are incorrect, as the Republicans support free territories while the Democrats uphold the Fugitive Slave laws. Option D is also incorrect, as the Republican platform promotes Homestead rights in the west without specifying citizen-only access.