Which letter follows mīm sākinah in «وَيَمْنَعُونَ»?

Al-Māʿūn and Al-Humazah: Applied Assimilation, Concealment, Madd and Hāʾ Rules

• Bāʾ, giving concealment
• Mīm, giving assimilation
• Lām, giving iqlāb
• Nūn, giving clear mīm