焊条直径的选择主要取决于（）。
A.焊接速度
B.被焊材料
C.焊件厚度
D.结构的要求
参考答案：C
A ship under construction or major repair will acquire permanent magnetism due to（）while sitting stationary in the earth’s magnetic field.
A.hammering and jarring
B.vibration and pounding
C.varying magnetic fields
D.stable or permanent magnetism of the ship
画趣
