A.350mm B.300mm C.400mm D.450mm
A.應(yīng)先退后進(jìn) B.應(yīng)先進(jìn)后退 C.應(yīng)同時(shí)進(jìn)退 D.上述都正確
A.小于8mm B.大于12mm C.大于15mm D.小于8mm大于12mm