裂纹在射线探伤底片上呈现略带曲折或直线状黑色细条纹。( )
参考答案：对
The poor old man _______ last week, his _______ made everyone sad
A. dies, dead B. dead, dying C. died, death
在无冰冻地区，埋地铺设时，管顶的覆土埋深不得小于( )mm。
A．50B．60C．70D．80
