51.  NATO spokesmen said they had no information about such an attack.

52.  New studies suggest the risk of such an attack is great.

53.  Neither nation has developed a sophisticated system for launching such an attack.

54.  No one could reasonably have imagined such an attack taking place in Japan, they say.

55.  Nunn painted a grim picture of how easily such an attack could be launched and how poorly the United States is prepared.

56.  Not surprisingly, the Blue and Gold teams each replied that their designs would help minimize damage from such an attack.

57.  Once such an attack became known, Haley added, thousands of people could show up at hospitals claiming symptoms.

58.  On Friday, allied jets dropped precision-guided weapons on a radar installation in the northern zone, the first such attack since February.

59.  Other scientists said that much less sophisticated software could have predicted crucial elements of how the towers would behave in such an attack.

60.  Putin acknowledged the growing risk of such an attack, but he told Clinton that the United States has exaggerated the threat.