A.先點(diǎn)火再開(kāi)煤氣 B.先開(kāi)煤氣再點(diǎn)火 C.邊開(kāi)煤氣邊點(diǎn)火
A.中心線裂紋 B.縱裂 C.夾雜
A.50mm B.100mm C.150mm