防烟分区的挡烟垂壁，应采用（）装修材料
A、A级
B、B1级
C、B2级
D、B3级
参考答案：A
I feel proud to be born into a family education is highly valued.
A．where
B．that
C．which
D．who
牙周膜的厚度约为（）
A.0.01～0.38mm
B.0.10～0.38mm
C.0.05～0.38mm
D.0.15～0.38mm
E.0.20～0.38mm
