51.   Pak withdrew this week to be with her sister, Yoo Ri Pak, who was in midtown Manhattan when the twin towers fell.

52.   Searching for clues, frame by frame, engineers studying the collapse of the World Trade Center have seen the twin towers fall hundreds of times on videotape.

53.   Sumeira Ullah, a junior, was at her eighth-floor campus job when the towers fell.

54.   The firefighters had gone into the apartment house about two hours after the first tower fell to make sure that it had been evacuated.

55.   There were reports of an explosion soon before the tower fell, then a strange sucking sound, and then the sound of floors collapsing.

56.   Those inside had just under an hour to escape and no apparent warning that the towers might fall.

57.   When the towers fell, Cray said, he locked away his manuscript.