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    LONDON—Terror struck in the heart of London on Thursday as explosions ripped through three subway trains and blasted(炸开)the roof off a crowded red double-decker bus. At least 37 people were killed and more than 700 wounded in the deadliest attack on the city since the blitz(闪电战)in World War II.

    British Prime Minister Tony Blair blamed Islamic extremists and said the bombings were designed to coincide with the opening in Scotland of a G-8 summit of the world's most powerful leaders. Foreign Secretary Jack Straw said the bombings—which came the day after London won the bid to host the 2012 Olympics--- have the “hallmarks(特点)of an al-Qaida-related attack”.

    Trapped passengers in the Underground railway threw themselves on the floor, some sobbing. As subway cars quickly filled with smoke, people used their umbrellas try to break the windows so that they could get air. Passengers emerged from the Underground covered with blood and soot(黑烟). On the street, in a light rain, buses ferried the wounded, and doctors used a hotel as a hospital.

     “I didn't hear anything, just a flash of light, people screaming, no thoughts of what it was. I just had to get out of the train,” said subway passenger Chris Randall, 28, who was hospitalized with cuts and burns to the face, the legs and hands.

     “It was chaos(混乱),” said Gary Lewis, 32, evacuated(撤离)from a subway train at King's Cross station. “The one haunting(萦绕)image was someone whose face was totally black( with soot) and pouring with blood.”

    Police said there had been no warning and that the blasts at three subway stations went off within 26 minutes, starting at 8:51 a.m. in an Underground train just outside the financial district. Authorities initially blames a power failure but realized it was a terror attack after the bus bombing near the British Museum at 9:47 a.m.—less than an hour after the first explosion.