建设工程档案
参考答案：
在工程建设活动中，直接形成的具有归档保存价值的文字、图像、声像等各种形成的历史记录。
It was so quiet in the classroom that a needle _____ to drop onto the floor. [ ]
A. could hear
B. was to be heard
C. could have been heard
D. must be heard
危险品库、压力容器、储油罐等则是固定源，但其区域范围不固定。
