A.圍巖必須堅(jiān)硬穩(wěn)固B.礦體必須堅(jiān)硬穩(wěn)固C.圍巖必須允許崩落D.以上都不對(duì)
A.礦體堅(jiān)硬B.圍巖堅(jiān)硬C.礦體與圍巖均穩(wěn)固D.條件不限
A.0°B.30°~55°C.≤25°D.≥55°