第一节：完成句子（共10小题；每小题1.5分，满分15分）
阅读下列各小题，根据括号内的汉语提示，用句末括号内的英语单词完成句子，并将答案写在答题卡上的相应题号后。
71. Only when the meeting began ____________ ( 他才意识到 ) that he had left his paper in the office. (realize)
72. Rescuers________ ( 担心)the safety of the children trapped in the dangerous building when the earthquake happened. (concern )
