多层焊时，逐层锤击可以使焊缝产生塑性变形而降低残余应力.因此，锤击焊道表面可以提高焊缝金属的力学性能，特别是（）.
参考答案：冲击韧性
—Where are Tom and Mary?
--____ Tom _____ Mary is busy with their homework. You’d better play with.
A．Both, and
B．Neither, nor
C．Either, or
D．Not only, but also
红细胞内缺乏G6PD的患者使用可产生溶血的药物是：
A．氯喹
B．奎宁
C．青蒿素
D．伯氨喹
E．乙胺嘧啶
