单项选择题

A.开槽支撑,先撑后挖,分层开挖,严禁超挖
B.开槽支撑,先挖后撑,分层开挖,严禁超挖
C.开槽支撑,先撑后挖,分段开挖,严禁超挖
D.开槽支撑,先挖后撑,分段开挖,严禁超挖