You mustn't _____ until he comes back.[ ]
A. be away
B. leave
C. be left
D. have been
B
伤寒较为常见的并发症是__________,最严重的并发症是______________。
当低碳钢试件的试验应力σ=σs时,试件将:()
A.完全失去承载能力
B.破断
C.发生局部颈缩现象
D.产生很大的塑性变形