根据《国家电网公司输变电工程标准工艺（三）工艺标准库》的要求，屋面防水等级为Ⅱ级的防水层合理使用年限为（）年。
参考答案：15
It was quite a serious mistake, ____caused by carelessness.
A．which I think was
B．I think which was
C．which I think it was
D．I think which it was
狱情排查的方法主要有（）。
A.情况汇报
B.心理咨询
C.个案分析
D.日常观察
