I had them take their backpacks and put them over their heads, just as another safety precaution, as they were down in the center of our room, in the center of our building.
我让他们把背包顶在头上，就像另外一次安全预警一样，然后集中到教室的中心，整栋建筑的中心。
2
Codes for tall buildingsafety were found to be deficient following the World Trade Center collapse in 2001.