How does the Apostle Paul's appeal to Philemon regarding Onesimus (Philemon 1:8-20) challenge the social norms and legal structures of the Roman Empire regarding slavery?

A Paul explicitly demands Philemon to immediately free all of his slaves as a condition of their Christian fellowship. B Paul subtly undermines the institution of slavery by advocating for Onesimus to be received not as a slave, but as a beloved brother in Christ, implying equality and mutual respect. C Paul reinforces the existing social hierarchy by reminding Onesimus of his duties as a slave and Philemon of his rights as a master. D Paul avoids addressing the issue of slavery altogether, focusing solely on the personal relationship between Philemon and Onesimus.