Which excerpt expresses the principle of states' rights?

A."There are certain issues, such as slavery, that should not be decided by the federal government."
B."Slavery is morally wrong and slaves must be given their freedom. Steps should be taken to ensure their political well-being."
C."The Union is perpetual and must be preserved by force if necessary. Secession is both illegal and unconstitutional."
D."The nation's wounds will heal most quickly if we forgive the Southerners and welcome them back into the Union."