A . 层高不大于5m时为6mm,层高大于5m时为8mm
B . 层高不大于5m时为8mm,层高大于5m时为6mm
C . 层高不大于5m时为7mm,层高大于5m时为5mm
D . 层高不大于5m时为5mm,层高大于5m时为7mm