71.   National Transportation Safety Board investigators have said that they believe a mechanical flaw caused an explosion in the center wing tank, which was nearly empty.

72.   Nonetheless, the strains that caused the explosion last week are still powerful, and Palestinians say that the best they have achieved thus far is a temporary truce.

73.   Nemtsov said in Moscow on Thursday that the explosion had been caused by a radio-activated land mine, and he immediately threatened to cancel the agreement.

74.   On Friday, officials involved in the investigation said initial examination of the probes showed that they did not cause the explosion.

75.   Parliamentary aides said the explosion was caused by a hand grenade that rolled in through the office.

76.   Police spokesmen said initially that they did not know what caused the explosion.

77.   Popov said Friday that much of the damage was caused by an explosion, but he did not know what caused the explosion.

78.   Pemex did not know what had caused the explosions but would investigate.

79.   Some fire department officials said that ammonia and other refrigeration chemicals could have caused the explosion.

80.   Taylor is the better short-story writer because he deals in fraught encounters and situations, the moment when contraries meet and cause an explosion.