A tractor-trailer hit and killed a man as he crossed a Brooklyn street Monday morning, police said. The man, who’s believed to be in his 20s, was crossing Flatlands Ave near 79th St in Canarsie and was mid-block when the truck slammed into him around 4 Am, cops said. Police officers who arrived at the scene discovered the man laying on pavement with trauma to his body. Medics rushed him to Brookdale University Hospital, where he died. The driver remained at the scene and isn’t expected to be charged.