CAIRO, May 6 (Reuters) - Three people were killed on Sunday when a 4-storey apartment building collapsed in a poor neighbourhood of Cairo, security sources said. They said two bodies had been pulled from the rubble, and authorities were working to recover the body of a third person from beneath the wreckage in the working class Sayyeda Zeinab neighbourhood. Building collapses are a frequent hazard in poor parts of Egypt because of lax building standards and poor maintenance.