烧穿
参考答案：
烧穿指焊接过程中，熔化金属向坡口背面流出形成穿孔的缺陷。
— I expected him to be nervous before his interview, but he was as cool as a cucumber.
— He____ it seriously. [ ]
A. should have prepared
B. might have prepared
C. must have prepared
D. can't have prepared
根据《烟草建筑设计防火规范》，烟草建筑的生产及储存物品的火灾危险性类别为（）类
A.甲
B.乙
C.丙
D.丁
