【单选题】
钢筋混凝土梁受拉区边缘开始出现裂缝是因为受拉边缘（ ）。
①
受拉混凝土的应力超过混凝土的实际抗拉强度
②
受拉混凝土的应变达到混凝土的极限拉应变
③
受拉混凝土的应力达到混凝土的抗拉强度设计值
④
受拉混凝土的应力达到混凝土的抗拉强度标准值
【单选题】
化工制图中图线宽度分粗、中粗、细三种，若粗实线的宽度为d，则细实线的宽度为( )。
①
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2d
②
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d
③
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1/2d
④
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1/4d
【单选题】
焊缝局部热处理时，每侧母材的加热宽度及接管外围母材的加热宽度分别是：（ ）。
①
A.母材厚度2倍和接管，母材中较大厚度的4倍
②
B.母材厚度4倍和接管，母材中较大厚度的2倍
③
C.母材厚度2倍和接管，母材中较大厚度的6倍
④
D.母材厚度6倍和接管，母材中较大厚度的2倍