Which would be general the least angular distortion when welding a 50 mm thick plate 当焊接50毫米厚的板材时，哪种方法的角变形最小

A、
single v preparation using MMA
B、
single v preparation using MIG使用MIG的单V准备
C、 square edge open butt using electrol slag welding使用电渣焊的方边开口对接
D、
single u preparation using submerged arc welding使用埋弧焊的单U准备