埋弧自动焊，当熔渣粘度过大，使熔渣的______性不良，熔池结晶时______排出困难，使焊缝表面形成许多______，成形恶化。
参考答案：透气；气体；凹坑
用所给单词的适当形式填空。使句意完整、正确。
1. There are ten ____________ (box) in the classroom.
2. Children's Day is on the ____________ (one) of June.
3. Tom's schoolbag is ____________ (heavy) than Jim's.
4. Is this postcard yours? No, it's ____________ (her).
5. Liu Tao and his mother ____________ (go) for a walk after dinner yesterday.
已知一元二次方程x2-6x+5-k=0的根的判别式△=4，则这个方程的根为______．
