The key you have just got     the front door.

A．is used to opening

B．is used to be opened

C．is used to being opened

D．is used to open

( )钢筋混凝土结构旋转楼梯钢筋支模法操作工艺中底板的铺设方法：底板材料用纤维板，先计算出内、外圆弧的尺寸并划在钢筋筏上。然后在钢筋筏上拼复，用钉锥在纤维板上钻出小孔，穿细铁丝与钢筋筏绞紧。