safety board短语⁹⁶⁶⁷⁷⁺⁶ 基本例句 安全台 In 2008 the National Transport Safety Board concluded that extra concrete, which had been added to the bridge over the years as the level of traffic increased, had helped cause the collapse. 2008年，美国国家运输安全局推断这些年来大桥的车流量升高增大了桁架的负荷是导致桥坍塌的原因。 ecocn