Divers retrieved four bodies after a sand-laden cargo sank in the Burigranga River here early Friday.   The deceased were identified as Babu, 19, Mostafa, 55, and Mohibullah, 60, of Pirojpur and Lutfar Rahman, 40, of Jhalakati.   Shah Zaman, officer-in-charge of Keraniganj Police Station, said the sand-laden cargo, waiting for repair work at the dockyard, sank around 3am near Afaz Dockyard, leaving its four staff dead.   He said two masters of the cargo, Taslim-1, swam ashore.   On information, divers went to the spot and retrieved the four bodies, said Imran Hossain, an officer at Shyampur Fire Service.   The bodies were handed over to Jajira Police Outpost, he added.