题目内容

Plain carbon steel has good ductility and weldabllity if its carbon contest is () and a high yield strength if its carbon content is().

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作业按其层次可分为四种,下列作业中作业的成本与产品的数量成正比的是()

A. 单位水平作业
B. 批次水平作业
C. 产品水平作业
D. 维持水平作业

The principal characteristics of timber are()、()、()

Strength of timber is affected by four main factors, they are()、()、()、()

The endwise strength of timber is much stronger than the band strength.

A. 对
B. 错

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