They became friends again that day. Until then they ______to each other for nearly two years.

A．didn’t speak

B．hadn’t spoken

C．haven’t spoken

D．haven’t been speaking

对钢板厚度大、焊缝尺寸较大、焊缝长和平焊位置较多的钢结构焊接，尽量使用什么焊条( )。

A．高效铁粉焊条

B．专用焊条

C．立向下焊条

D．低氢型焊条