Only when the villagers were faced with water shortage___       how serious the problem of water pollution was．

A．did they realize

B．will they realize

C．they did realize

D．were they realized

现有一框架结构工程，桩基础采用CFG桩，地下室外墙为现浇混凝土，深度5.5m，地下室室内独立柱尺寸为600mm×600mm，底板为600mm厚筏板基础。地下室防水层为SBS高聚物改性沥青防水卷材，拟采用外贴法施工。屋顶为平屋顶，水泥加气混凝土碎渣找坡，采用SBS高聚物改性沥青防水卷材。

层面坡度小于（）时，卷材宜平行屋脊铺贴。

A．3%

B．5%

C．8%

D．10%