---What did you discuss just now?

---We discussed           .

A．when could we meet at Xinhua Bookstore

B．where we would have a wonderful outing

C．whether we will have a barbecue during May Day

D．who is suitable to be the host of the charity

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