BRUSSELS (AP) — After a four-day shutdown prompted by a threat alert across Brussels, schools are reopening their doors with the help of beefed up security, including police armed with machine guns. At other schools in the region, officials sent parents letters and emails explaining security measures being taken under police orders, like limiting access to the school and not allowing children to play or gather in large spaces like courtyards. Some children looked visibly worried as they arrived at the upscale Brussels school but most gave a friendly handshake to a burly school official guarding the entrance alongside the police officers.