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问题 单项选择题

产生焊接应力和变形的根本原因是（）。

A、受到外力作用

B、结构刚性过大

C、不合理的焊接顺序

D、受到不均匀加热和冷却

答案

参考答案：D

选择题
At an Expo-themed forum in Shanghai's Yangpu District, Governments were also urged _____ a good job in protecting local old buildings and culture while pursuing social and economic development.

A. doing
B. having done
C. to be done
D. to do
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选择题

在卫星云图上，绿色一般表示[ ]

A．海洋

B．湖泊

C．云雨区

D．陆地

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